Hmmmm.... that's a good question. For us, it turned out that all the coaches recruited my son from HF and Stanford were head coaches. I can't recall a significant interaction with an assistant. (and I'm not counting camp invites as significant)
I'm just guessing but I would imagine that in most cases an assistant is at HF because either A) they are not actively still recruiting the current class or B) the HC trusts the assistant's judgment on players' completely, especially if the player has video and other evidence as well.