If you find that the simple collisions generated for the various cliffs assets from Megascans are too generous, and that your character is off againt an invisible wall, you are not alone (or maybe it is just me …).
Instead of using 26DOP Simplified collision, I found that it is way better to use the Auto convex collision option. I suggest to try and experiment with the 3 values (Hull count, Max Hull Verts, and Hull Precision).
I personnally settled for 10 / 16 / 300000
26DOP Simple collision
Auto convex.
And use complex collision for the slabs.