I believe when it clamps to ground it uses whatever LOD is currently loaded, so it shouldn’t sink into the ground. I think another approach that I used recently was to set the height reference of my entity to relative to ground instead of clamp, so I can set it a few pixels above the ground to make it look nicer.
Try it out, and if you can get a Sandcastle example (you can click the share button to get a link to share) of how it looks if it doesn’t look great, that could help a lot in providing us a test case that we can use to improve Cesium.
Thanks again!