I'm tiling a tub deck prior to installing the tub due to a lack of space to insert tiles on the back and sides. I can't install the apron tiles because the plumber needs access from there. So, my question is: How far do I overlap the deck tiles in the front to accommodate the apron tiles? The width of a tile plus something for the mortar? I'd like this edge to be as near perfect as possible as it's the most visible in the room. Thanks.