I just installed a steel tub, put HardieBoard up, mudded the joints, and now I'm ready to tile. Here's my question: since the tub slopes, on each of the sidewalls, on the high side I am 1/8" off the tub with the Hardie Board (level)on one end, and around 1" on the other end. On the 1" end, I am 1/4" above the tub flange. Since I need my tile to be level as well, am I supposed to fill that whole 1" gap with silicone?!