Comment 1 for bug 896166

I noticed this problem too, but I don't think this can be fixed easily. YR is not a 3D engine, and it won't understand that those lower parts of the cliff should become brighter with height.

The reason for this is because cliffs are in fact objects made from 2 images (sometimes even more) - 1 is on top, and 1 is at the bottom. They're just made to look like 1 object. The RA2/YR engine simply applies the bottom level's lighting to the bottom part, and the top level's lighting to the top part, without any room for anything in between.