It doesn't look like the rule tile system supports large cliffs/walls in a nice way (I assume that's the part you're having issues with), you might need to set up 2 rule sets: 1 for the top layer of the terrain and one for cliffs.
I'm not too familiar with rule tiles in Unity but if you want to chat more about it/have more questions about the pack, feel free to contact me on Discord! Username: iClaimThisName