Installing new tub-tile-shower-faucets and am wondering if there is any built in leeway. What i mean is that the installation directions show "finished wall" Does this mean with tile, or can I rough-in to the backerboard? I'm just wondering if I need to figure in the thickness of my tile or is there usually some fudge-factor built in to the design? Sorry if this is a dumb question. My faucet set is an American Standard single-handle design. Any hints would be appreciated.