replaced fiberglass shower pan and now ready to tile walls with ceramic tile. Should the bottom of the tile rest on the shower pan or should there be a gap. I know that area will eventually be caulked. Also, how much space can be between grout lines. One side of wall is okay but on other side the tiles would need larger grout lines or I would have to do a larger tile and cut it to size to come to the edge of shower pan. only about 1/4 inch or less off.