I find it hard to believe that any association would advocate whacking a coach just because he was standing within the legal confines of the box. At what point do you call it? When he stands for 5 seconds without talking? 10? 30?
Are you paying that much attention to the coach and not the game, to see if he isn't saying something to his players? What if he was instructing his bench personnel and not those on the floor.
You'd have a hard time convincing your assigner that this was a legit foul call.
I'd like to be in the stands the first time you called this on a coach.