Robb said
I want to point out that for some people the "proper part of the fist" may be a very different part depending on your body alignment. There was a long thread on this awhile back that, for the seiken in particular, the wrist position covers a wide, wide range. And that for many if not most women - the ideal alignment for a seiken will have the first two knuckles lined up with the bones in the arm.one should also be very careful to make contact with the proper part of the fist or other weapon when hitting objects.
I've also seen quite a range of how people align their thumbs and hands to do the bushiken strikes.
So there is a lot of variability in my mind in "proper" - each person needs to find what is proper for their body.