Maybe it is implemented this way, but it'd be cool if province wasn't necessarily all forest/mountain/etc., but as with rivers, it'd be forest/mountain/etc. on the border with another province. For example province A has borders with provinces B, C, and D. Province A is mostly forest terrain, so is border with province B. But its border with prov C has mountain terrain and the one with prov D has hills terrain. There is also river between provinces A and B. So, when province A is attacked from province B, it qualifies as forest with river crossing. When from prov C, it is qualified as mountain and from D as hills. Vice versa with attacking from A to B, C or D. If province A is enveloped and attacked from multiple directions, units bonuses and penalties always depend on the fact from which direction attack comes.
It needs little more thinking before it is usable, but it'd be logical and not that hard to implement given we use this kind of thinking, but only for three special occasions - river crossing, amphibious assault and paradrop.
It needs little more thinking before it is usable, but it'd be logical and not that hard to implement given we use this kind of thinking, but only for three special occasions - river crossing, amphibious assault and paradrop.