Technically, "%20 cooler" means "120% of the coolness of something." So you take a fifth of the coolness of something and you add that amount back on to the original. Which is interesting, actually, because it means if something is not very cool to begin with, it won't have much coolness added on to it, just a little bit, but if something is already really cool, then it gets a huge boost in coolness. And "20% cooler" only takes into account coolness, it's independent from the amount of swag, sexiness, etc., unless one of those factors has a relationship to the coolness factor, which I don't think they do. Rainbow Dash was clear in "May the best pet win!" that there is a big difference between radicalness and awesomeness, so the same probably goes for coolness, so they are probably unrelated factors.