Not being able to remember anything specific from my own experiences; but do enemy (read AI) troops use covered avenues of approach (such as moving through woods instead of roads, etc.) ? It seems as tanks and other vehicles tend to use roads, but what about infantry ?
They will advance toward the objective the best path they can find. If there's a road there, they will use it IF it gets them to where they want to be quicker otherwise they will seek out the path of least resistance but only based on how they can get from A to B on that turn so the AI won't be looking 5 turns ahead