I've read in many FAQ's that Tifa's final weapon, the Premium Heart, is powered up by getting lots of 'Miss' icons on her Limit Break slots. I have played the game through many times, and found that her weapon grows in power in conjunction with her limit bar, that is to say when she has almost got a limit break her weapon is more powerful. I have the English version of the game, so is it different from the North American version, or have either the FAQ's or myself gotten something wrong?