I know it's a slighly different problem, but didnt want to make a new topic about it since it's also about NPCs movement.
So what i noticed is that atm if a player manages to climb on some object like 5-10yds above the ground level the NPCs won't attack him anymore with melee, and that opens the possibility for some exploits, like in Hyjal for example in the horde encampment, if a player climbs on the top of those spike looking fences then the bosses would stop melee him and casts only the ranged spells. I know in the past the NPCs would "fly" and chase the players until a certain height, is it possible to get that back, maybe as a configurable height treshold?