Elements often get placed at the wrong Z value when working in 3D. It would be helpful to have a set Z value tool.
This would

Set the selected (fenced) elements to the defined elevation.
In the case of 3D elements, the lowest part of the object would be set at the specified elevation
Provide a toggle to planarize elements to the specified elevation. This would flatten polygons that are non-planar, move all vertices of linear elements to the elevation, make circles the same radius but at the specified elevation