This is especially prominent when you're the elves and every area the barbs walk into gives them defensive buffs.
Which - and this leads into the other Ljosalfar thread going on - leads me to think that perhaps certain races shouldn't suffer fighting units on tiles/areas they are really familiar with.
Elves fighting an enemy in a forest shouldn't have to deal with a defensive bonus the enemy gets in a forest. That is the elves favourite type of terrain, and they should be better in a forest than everything else.
Ditto for Dwarves in hills. Lizards in jungles, Orcs in jungles etc.
I guess it might be too hard to split that up though...ie Elves fighting Barbs who are on a forested hill...Barbs would get 25% from the hill, but not the 25% from the forest. Could be too much coding in there if it's even possible.