How do fortifications affect defensive modifiers when used in non-clear terrain? Is the effect cumulative? For instance, is there any point in digging-in in a forest hex?
The forest hex has a -30% defensive modifier while the fort has a
-20% modifier. So if you dig-in, do you now have a total -50% modifier? Or have you actually made your position worse by reducing the existing -30% of the forest to the -20% of the fort?
Yes the modifiers are cumulative. The best choice would be to choose a hex with high defense (the highest is usually city or industrial hexes) then dig your units into TRENCHES.
I think terrain that follows hexsides do modify assaults? Such as creeks, wadi's, etc. Also, unsupported armor units have their assault values modified by the terrain in the hex if it is not clear. But without looking, I think it is just a straight half, regardless of the type of non-clear terrain??