Extruded entities dont have equal distance to ellipsoid surface (height)

Hi all,

how are entities along the curvature of earth calculated internally? I assumed that setting up an entity and extruding it would lead to the entity having the same distance relative to ground (being of equal height everywhere). But this is clearly not the case.

Sandcastle Example

I would expect the rectangle in the example to have the same height everywhere. Is this expected behavior? Is there anything I can do about it?

Thanks in advance.