I have a 300sf entry room and have put down 1/2" Durock with modified thinset and screws over plywood. The plywood is 23/32" sturd-i-floor glued to 2x12 spf spanning 12 1/2 feet. The floor seems very solid. I have already purchased Ditra Heat because I like how the heat cable snaps into the grid and was wondering if it would be ok to install over the cement board? If so, What would be the preferred thinset to use? My tiles are 12x24 Ceramic.