I think your "dark-up" shadowing definately looks great (which I why I tried to copy it!).

You did invoke Tolkien, which for me wins any argument, but here's one additional potential rationalization of the light. The moutain is darker near the top because it's STEEPER, and as it rolls off it "sees" more of the ambient sky-light and is lighter. It's more of surface-angle dome-light issue than a point light-source i.e. the sun.

Eh? Maybe?

Either way, your map is looking great. And you are right, I do struggle with the mountains-on-a-map-as-a-perspective vs. mountains-as-icons. The temptation for the simulationist in me is to draw the satellite-view style ranges, but I just don't like how that looks as much.