Hi @mhrmsg,
Thanks for your post and welcome to the Cesium community.
This forums thread covers how to clamp a tileset to the ground when using terrain 3d tileset clamp to ground.
I am curious if in your current setup the tileset is fully or partially occluded by the terrain? I expect the guides linked in the forums thread will address your question, but please let us know if now and we would be happy to help further.
Best,
Luke