Mount Bounding Box Annoyances

Okay, so:

Have a flying broom.  It has a nice little bounding box, player sits on it, all is well.

But the broom can fly into ceilings or gaps that are small enough that the rider goes into the ceiling and gets hurt.

So, I expand the bounding box to just be taller than the whole player + mount?  Great!  Works lovely!  Oh, but now everything the player does targets the mount, because (I think) the player is inside the bounding box of the mount.

Sooooooooooooo....   Is there a way to get "The mount stops before spiking the player's head into the ceiling" and also "the player can target things while mounted" that anyone knows?