Funny AI

[pezhetairoi]

But recently I haven't been able to pull off that trick. Now instead of wheeling off the high ground, the enemy goes on the offensive once I wheel off his flank so the best I'm able to pull off is both of us, half-on and half-off the high ground.

[Bellum]

Even so, depending on the situation you should be able to get some of your forces to get on the higher flank after the opponent is otherwise engaged.

EDIT: I suppose it depends on the steepness of the hill. Sometimes, with the amount of time it takes to get the forces up there and rest out of uselessness, it just isn't worth it.