We have a steam shower, with a bench that runs the width of the shower. The shower is tiled in travertine tile, the bench seat is granite. The seat that finally got installed slopes 3/4 in from back to front. I feel like I am sliding off the seat. The contractor tells me that 3/4 in (over the 16 in depth) is a reasonable slope. This is the second seat to be installed - first seat came in too small, but was not sloped as much. In reinstalling the new seat, was told that they had to slope it more so as not to damage the liner for the steam shower. Is the contractor right?