Height might be a strange feature in a 2D game, but it's here and is going to stay. Have you seen people shoot through walls but you couldn't shoot back? It's not hacking, it's height. For example, a player (whose height is 20) next to a wall (whose height is greater than 15) can shoot "past" that wall. A great in-game example would be the game "CTF Zone Alpha". In CTF Zone Alpha, you can shoot past walls (if you are behind one) but cannot if you are on the grass.
(For reference, the default height for a player is 20 (plus the weapon they are holding)).