I am seeing some strange behaviour here. Attached is my current file, some additional operations but it is the PathShape which looks strange.
Just playing with Z on SketchEngraveLines, I can change Z in Attachment but not in Base. If I change Z in Attachment then Z Base changes, but not by the same amount, except that if I change it to zero then Z Base does not change. The g-code Z seems to be the difference between the two.
I assume that this is a bug, or have I missed something.
This is not a show stopper for me, I can fairly easily reset Z on my machine to compensate.