Directing character's fist to a specific position

Hey, I'm working on a boxing VR game and i encounter that problem:

I have a character of a fighter that from time to time attacks the player in a different attack (right punch, headbut, left hook and more).

the problem is: the players head is allwayes at different heights (people have different height) and the punching animation is always pointing the same place.

what I want: I want the character's fist to get directly to the players head.

tried using target animation but didn't quite got it.

Thanks a lot!