Thanks, Matt. I've got it to work, but not by ticking world space. That actually doesn't change whether it works or not, but you have to use 'position in terrain/texture' in the second SS. Why didn't I think of that before
And you don't need an X redirect, but a simple displacement shader will do after compute terrain. One thing that eludes me is that if you set Z rotation to 90 degrees, the displaced square/second SS is located slightly below where its center is. Even if you set compute terrain to patch 1 or tick smooth terrain. You have to turn Z 115 degrees or so to get it on spot.
