in any style of wing chun, the bottom 3 knuckles are used every time and it may look like boxing punches are more powerful but this is a common misconception. it takes while to develope a proper wing chun punch but it is well worth it. it travels relaxed in a straight line making it much more energy efficiant. this may look weaker but a wing chun punch can maximize its damage at a range of just a few inches. thats why it has the reputation of being the most dangerous art up close. look up some of bruce lee's famous 1 inch punches, those are actually wing chun punches. if developed well enough, the punch can give enough explosive power from the elbows to send the guy flying 5 feet back from just inches away. they just have a different type of power, for example, when you hit a punching bag with a boxing punch, it will swing away from you as if you where to push it. a wing chun punch would make it vibrate really hard as apposed to pushing it. you do not need to throw your whole body into your whole body into your punch, you'd just be wasting energy. think of it like throwing a ball. would you tense your whole arm up and throw your whole body into it? of course not, you'd prlly end up hurting a muscle. relaxation is the key.