It appears from the image that you're doing things more or less correctly, although I'm wondering about the need for the Compute Terrain there. If you're applying heavy displacement in any of those nodes above it then it should probably just go in the Terrain group, before the original Compute Terrain, and if there's no heavy displacement then it's unnecessary.
So, aside from that slight oddity, it's hard to say more without actually seeing the .tgd. Would that be possible?
- Oshyan