Where it applies in Stony Cliffs Are Cool

The rule runs across every overworld biome rather than being tied to a particular climate, so the effect follows the terrain instead of the weather. You will see it most on ridgelines, plateau edges, the sides of river valleys and around the rims of lakes - anywhere the ground has been cut steeply.

Flat biomes simply have less steep ground, so they show less of it. That is intentional: the effect appears where a cliff would actually form.