Hi-- I will be installing a wood stove (morsoe 2b classic) and for ember protection I have an oversize (30x60") 3/8" thick porcelain tile and 11 cm hardie backer board. To minimize the risk of stubbing toes on it, I want to recess it by removing the floorboards and laying it on the subfloor. My question is, do I need to actually set the tile or cementboard or can I just lay them on top of the subfloor since they are each one piece? I'm not concerned about them moving, for obvious reasons, I just want to minimize the risk of cracking. Thank you!