There doesn't seem to be much consistency between commands that affect elevation. When using a command. Sometimes it will pick up the elevation of the snap point, sometimes it keeps the elevation of the original object and sometimes you have to enter the elevation at the keyboard. A lot of time the OSNapZ setting is ignored.
See: https://forums.autodesk.com/t5/civil-3d-ideas/feature-line-grip-edit-elevatoin-toggle-setting/idi-p/...
A good example is the Move Point in a Surface. Being able to let the pont assume the elevation of the snap point would make then using the Edit Point command to change the elevation.
I would recommend that all commands that work with Surfaces and Featurelines (at least) be standardized to have an option in the command to set whether the elevation of the snap point is used.
