I am installing a shower faucet and have the drywall removed exposing the vertical studs and am attempting to physically install the Delta Faucet MultiChoice R10000-UNBXHF Universal Shower Valve Body. I am finding installation instructions are little confusing to say the least. I will be replacing the drywall and building a membrane using 1/4" Hardie backer board on the three walls and floor then tiling. I understand that I have to install a cross piece between the studs to screw the valve base to and my question is that the face of the silver bezel seems to have to be flush with either the hardie backer board or flush with the tile. The black plastic square part that clips to the valve housing, not quite sure what it's for. My concern is once the drywall, hardie board and tile is up it's a bit late to find it should have been 1/4" further out. Hoping there are a few that have done this and point me in the right direction. Many thanks.