If you look at photos of sheer/steep cliffs IRL, you'll find that they have layers, they're often staggered and have both gaps/dips and parts that stick out. There are often bits where earth can accumulate and plants grow. I think you'll have an easier time designing your tiles if you start with a simplification of the forms found in reality, rather than trying to apply a "rock texture" to your existing walls.
Edit: Check out the game Mandagon, which has very stylised cliffs. They're very blocky, and all the staggering is for playable areas, but perhaps it might give you some ideas. Of course, the rest of the game is stylised to match. You seem to be going for a more realistic look with your trees and grass than the cliffs.