I think the module creates the battles randomly
somewhere on the map, not directly "on top" of you.
At least to me the word ambient means kinda the same as background, as in background combat..
I have no idea if it helps but maybe you can "direct" it a bit by adding locations owned by the enemy and friendly sides, might be that the module "sees" them and utilizes them:
Towns and villages have locations set to them by default so you can try changing the location side by adding "owners" (Units -> Game Logic -> Locations -> Owner XX) to the towns by placing them on top of the town.
I have no idea if this even works, there's a lot of stuff in A2 mission editing that BIS have not shed any light on so this is just theory so I'm assuming the game can somehow link the predefined location and the owner you set in the editor..
Or maybe adding a location object and then a owner object and synchronizing the two works
This is just a blind stab in the dark so don't quote me on any of this..