How are you cutting the xps? I was using my tablesaw for 2" foam and they seemed to be coming out almost perfect.The subfloors my from the floor above the basement is not plywood. It is made up of individual boards installed diagonally. Combine the unevenness of this subfloor design with nails that are popping and through and my own flaws cutting the xps, I wind up using a lot of caulk. I think it might just be easier to foam all the edges with the stuff in the can.