Mobs have no idea about height, as far as they are concerned you are on the same ground level as them, despite you being 10 floors up.
About a month ago I had an interesting time on WAR, found a recent dead tribe with 30+ revs in it, they acted normally most of the time, but every now and then something would change. Some would start to walk a lot faster than the rest, despite using the same walking animation, some would start to jog a lot faster too.
Then there was the different levels of agro, some revs would completely ignore me, others would run away from me, regular agro was there so you could get a bunch of them following you around trying to hit you (rev train), but if you had any of those that moved faster go agro on you, then they could be on you to fast and hit you several times before you realised it.
Then there was the weird one, like someone flicked a switch, every rev suddenly became "scared" if me, get close to any of them and they would run away, some ran that fast I was having a hard time keeping up. Hitting them like this was almost like being on the test server when mob agro has been turned off, they can be damaged and they react to each hit, but they just wont attack me back, instead they just keep running away, but after a couple of minutes the switch is flicked again and they are all back to trying to kill me.