[Imp]

Just my opinion but a map with few roads works better, the trouble is & I am not sure here the AI does tend to charge unless it is getting close to victory hexes, about 2 turns movement or less from them & vehicles will start unloading & move more cautiously.
Defending therefore if you are well in front of the victory hexes it never does this.
Placing them diffrently can help but needs real thought to make it work well.
example
A line of trees with VHs placed on the otherside the AI will unload & move to the trees on foot, of course if you are set up in the trees does not help it much.
Place a couple of flags further forward to trigger. Same with roads etc the odd flag on by the road will slow it.
As I said not sure about this its how I feel it works & the AI might decide to ignore the VHs go for flanks & sweep round so guessing where to place is tricky.
Also it does not like tricky terrain avoid maps with deep water & impassable terrain.

As Wdll said the only real option is a human or many many hours in the editor designing a battle.
This is simply due to the amount of factors you take into account when you play, probably though you dont realise it over a dozen each time you move a unit & thats impossible to program for. Its also why the game is intresting your brain is actually getting a bit of a work out.
Giving the AI the side with the better equipment is a work around esp if you need to get flank shots etc.
Also & I swear this is correct but it must be me one game in 3 or 4 the AI gets its act together & plays far better using combined arms attempting to flank found units etc.
If it starts the game that way seems to play that way through the entire game so the only thing I can think of is the map suites it.
Last thought map size makes a big diffrence
Width - the wider it is the more chance there is of fast units getting ahead of slower ones resulting in waves so very easy to deal with.
Depth - keep it sensible for the force size if you think you are spread out so is the AI most likely & its not good at moving units over to reinforce where needed. Again normally an easier job for you picking them off though on occasion it might decide to lump everything together a give you a nasty surprise.