i had a contractor build a hearth for the corner (2x4's, plywood) and along the two walls the plywood extends 4 feet from the corner. The problem is the platform is square but the corner is not so there is a wedge shaped space that is 1/2 inch from wall at 4 feet. I want to tile on top. How do I deal with the gap? There will be a heat shield 1" off the platform so the gap will show.