The screws piercing the PVC membrane are 1-3/4 to 2" above the PVC
membrane lying on the subfloor, but on top of the PVC liner a sloping
mortar bed will be added as one cannot place tile directly over the PVC
liner.

This means that after the tile on the shower floor is installed, the
screw holes will be much closer to the bottom of the shower floor than
the 1-3/4" to 2" that I listed in my original email.

Sorry for posting my inquiry so often. I had posted it and deleted it
several times - each time revising it a little.

Thanks.