How to properly use a terrain surface as an upper boundary?

[qingsonger]

Hi all,
I am trying to use a terrain surface as the upper boundary in a LoopStructural model. I have attempted to apply both add_unconformity、add_onlap_unconformity， but neither seems to fully prevent the underlying stratigraphic surfaces from piercing through the terrain.

I would like to ask if there is a recommended approach or best practice to ensure that the terrain surface acts as a strict upper boundary, so that all stratigraphic layers are properly truncated and do not cross it.

Any suggestions, example workflows, or references to documentation/discussions would be greatly appreciated!

Thanks in advance for your help!