Thanks. I think I'll edit the mid-ground, I've had it a few different ways before this, tried it with gentle rolling hills into the distance, tried it with no visible sky and a sheer cliff where the sky is now.
I'm going to take the lake back to a much smaller pond in a sheep field, I think I'll keep the background hills, I quite like them but I might adjust the constraints of the crossed stratas to bring more rock onto the steeper parts of the hills.