Hi. Replacing my 2nd floor bathroom floor. I removed the tile and cement board. I plan on installing Kerdi, then the tile. The toilet flange now sitting above the sub floor and the metal ring spins freely. without removing the existing flange and ring, how do I go about installing the Kerdi and tile? Can I screw the metal ring into the sub floor even though there is that gap between the floor and ring? Do I just cut the Kerdi around the ring and not under the ring itself? Advice is appreciated. Thanks.