We'll just handwave A2, it's not a big deal.
Also as long as we know who's riding what, there's no ambiguity in denoting a character and its mount sharing a square by either the character's symbol or mount's symbol, interchangeably (usually prefer the controlling character for obvious reasons—upscale for the mount). We can just add a note to the tile (right-click menu option) if it's still an issue.