So, I figured out (I believe) how to get this working for myself. What I did is a disp to scalar, divided it for some smoothness, than a colour adjust, -1000 black level and 2000 white level, both clamped. I than simply plugged that into the altitude adjustment. No difference, sure, than I headed into the cloud layer itself, and upped the Function Multiplier to a whopping 1500-2000 (in my scenes case) to get some effect. I haven't rendered this for a confirmation but it looks pretty obvious in the preview from the flat cloud layer cutting off the mountains half way up.