Here is an explanation quoted from someone on a forum (I am unsure as to which forum or the individual who originally wrote this):
The shishi houkoudan is based on the idiom 気が重い which means being bummed out/depressed, but literally means the ki is heavy. The perfect shishi houkoudan is based on 気が沈む, being gloomy/ melancholic, but literally the ki sinks, (hence the downward arrow on the scroll and Ryouga understanding when he sees the fish toy sink) that's why unlike the normal version the perfect shishi houkoudan drops down from above. The mouko takabisha is based on 強気, confident/aggressive, but literally strong ki.The power of ki blasts appear to be based on the strength of the emotion that they are being focused through and the amount of ki used. Shishi Höködan uses depression and Möko Takabisha uses confidence. Other emotions could probably be used as well such as anger/rage or fear. If a character can't focus on one emotion such as depression they aught to switch to a different emotion since that is exactly what Ranma did in the manga. Physical strength appears to have little to do with the power of the blasts -Ryoga's regular ki blasts did not decrease in size during the time he was made younger and Miss Hinako is not the physically strongest character.
After Ranma figures out the shishi houkoudan and before deciding on the mouko takabisha he tries out a couple of different puns/idioms/emotions, but they aren't particularly useful as attacks: Not feeling like it/ "the ki doesn't progress": The ball of ki sticks to his hands instead of flying away. Distracted/ "the ki scatters": The ball of ki scatters harmlessly.
Confused/ "the ki strays": The ball of ki comes back and hits him.
Impatience/ "short ki": a series of very small balls.
It probably is possible to use multiple emotions to power the blast and make them even larger so long as there is no conflict between them. I got this idea from the Rumiko Takahashi anniversary special which has multiple characters from her works interact. In the short Ranma appears to use a Shishi Höködan Möko Takabisha the way I see this working is because Ranma was depressed that he (well technically she) was groped but still had enough confidence to toss a confidence based one.
Ranma's standard Möko Takabisha has no charge up time and can be launched pretty much instantly. Ranma doesn't have to yell Möko Takabisha, nor does he have to be any special stance to throw it. The picture below shows Ranma throwing a blast over his shoulder mainly by accident without yelling Möko Takabisha (I do not know why I have not seen a fan fic in which Ranma is somehow restrained and tosses one out of his head or finger).
The blast can even be thrown as an extension to a punch.
These standard ki blasts are pretty hard to dodge when you consider they require next to no time to prepare (may need time to get in an emotional state but once in that state they can be launched repeatedly) they generally have a fairly large diameter with the standard blasts being larger than Ranma is tall, and they pack a punch (blows through brick walls with ease).
Ranma and Ryoga are not limited to throwing just one or two they can throw them repeatedly for quite a while.
While the power of the blast appears to be determined by the strength of the emotion it appears to be possible to vary the amount of ki used (Miss Hinako's blast became much more powerful when she accidentally drained ki from a bust of Principal Kuno). This means if they want a weaker blast they can be done by using less emotion or less ki (Ranma after all did throw a lot of very little tiny blasts while practicing). The reverses is true as well stronger emotion or more ki built up more powerful the blast - means Ranma can throw more powerful blasts if he feels the emotion stronger (imagine how powerful they'd be if he channeled his fear into a blast while near cats) or if he spent more time building up his aura prior to throwing them (Ranma has demonstrated the ability to build up his aura for example during the time he was at a hot spring island and it is an explicit ability of Ranma's in a few of the games such as Hard Battle).
Normal people in the manga probably can't see ki blasts at all or if they do they most likely see them as shimmers of heat. The reason I think this is because most people can't see aura's and we are shown that ki blasts are hot (not hot enough or possibly just not around long enough to cause things to combust - since fire requires both heat and time around the heat to start). This is shown in a few ways. Nabiki calls Ranma's little ki Blasts balls of hot air, Akane mistakes the heat from a hair drier for Kasumi's aura, Ranma and Ryoga's ki blast while children burnt the mushrooms of aging, and the way the Hiryü Shöten Ha works requires auras to be hot.
Ki does have some blow back Herb used the bounce back from his ki off the ground to do his flight trick and Miss Hinako used Ranma's ki to throw herself high into the air and to propel herself through the water.
The shape of ki blasts can be altered as well Herb used ki blasts shaped like crescents to cut.
Ki blasts maybe used as a steady beam by continuing to feed energy into the technique though this isn't really shown in the manga (Herb did have a whip like ki blast) but is shown in the anime.
Ki blasts are not compressed balls of air if they were they wouldn't have been able to pass through Ryoga when he didn't lose focus on the emotion. They would have hit him regardless of his emotional state.
Ranma can toss more than one at a time as demonstrated by the Möko Takabisha double.
I can think of a large number of possible variations to the technique as well as the battle auras and applications for the technique which causes me to often wonder why I don't see more in fan fics. Possible other variation smaller faster moving but higher density blasts. Doing a perfect Shishi Höködan and then taking all the energy wasted in the column and making a much more powerful blast. A barrage of small blasts. Using ki blasts as suppression fire. Propulsion as it had been in the manga occasionally (Ranma had Ryoga launch him farther by hitting Ranma with one, this type also appears as a move in the games, like Battle Renaissance, where Ranma uses the ki blast to propel himself like a canon ball into enemies). There are a lot of possible variations and times in which this would be very useful in combat but it is rarely shown in fan fics in other ways than how it was first shown. I sort of understand that because Ranma, hell most of the characters, rarely use ki blasts - many reasons for that such as too powerful takes away from the drama (I believe that is the reason stated by Takahashi in an interview for why Ranma doesn't use some techniques all the time but don't quote me on that since I'm not completely positive she said that), Ranma's tendency to fight at around his opponents level and in their style, it is over kill for most engagements, can be countered by ki blasts which makes it somewhat less useful against some opponents, etc.
The Shishi Höködan is focused through the emotion of depression. Since the technique is powered by depression and Cologne calls the technique a terrible one and that it's foolish to fight with it, some fans have adopted the stance that the Shishi Höködan actually induces despair, causing a martial artist who learned and uses it to become more and more depressed and melancholy. This is not the case. Cologne used the metaphor of two lions clawing at each other even as they tumble down a cliff. This is clarified to mean it's pointless to duel with the Shishi Höködan (as the worse you're doing, the more powerful it is — but the better you're doing, the less powerful it is, so the fighters just end up seesawing back and forth until they pummel each other senseless). Ryoga and Ranma prior to him deciding that depression isn't really an emotion that fits him (though considering how his life is you'd think it would be, Nabiki and Kasumi even comment on how his life is pretty bad) had to go out of their way to make themselves as miserable as possible for the fight. Ryoga's personality remained unchanged in subsequent stories.
I am annoyed when people attempt to place the characters on a hierarchy based on ki strength. There are a number of reasons as to why this bothers me. The first being they tend to place Saffron and Rouge's Ashura form on the scale when neither of them used ki attacks they used raw fire (as well as lightning in the case of Rouge). Second they tend to rank Miss Hinako very high on the scale when I find it debatable that she should even be considered since, while she has tossed some pretty powerful ki blasts, it is not her ki she's using she has to drain it from someone else to toss them. Third most of the characters don't toss around ki blast often or like the already mentioned Rouge and the not mentioned Ryu Kumon they aren't tossing around ki (Ryu tosses around vacuum blades and Tatewaki tossed around air pressure waves). Fourth some clearly powerful people like Happosai and Genma don't go around tossing ki blasts even though they can create massive sky scrapper sized auras. Fifth because of the nature of emotion focused ki blasts a less powerful person could toss a much larger blast than a more powerful person by simply reaching a depth of emotion that can not be matched by the other character. Sixth, and the last reason I'm going to give for now, Takahashi did not attempt to do so at all. Characters did not try to generally match each others power they tended to use techniques/skill/trickery instead (and in several cases it is quite clear had the character been using lethal force, brute power, strength, raw speed, etc. they could have overwhelmed the opponent) and several of the characters clearly limited themselves (such as not using lethal techniques).