sampleTerrainMostDetailed return wrong heights

Hi everyone!
The screenshot shows the problem i found, some sample points’s height higher that terrain surface, and some sample points’s height lower that terrain surface, anyone knows how to handle this?

Demo in sandcastle:

Before set Ground Translucency:

After set Ground Translucency:

I tried empty terrain, i have same height data as before, i’m confused how it works.

Thanks for the help