After all, I decided to use a completely different approach to achieve what I want. Not because I don't know how, but because it seems easier and more controllable.
I made another SSS-masked surface shader to make the path. I made it a bit wider than the main elevated terrain, so that a 3-5 meter path is created all along the wall, then, I'll just curve it like the main wall with the same exact redirect that I used for the larger structure. The good thing about SSS-masked terrains is that they are always smooth as long as they have an edge profile. Even if it's just a few centimeters...
An overhang can be conveniently made with a well-masked lateral displacement and I will add it too.