So I ripped up the 3/8 plywood subfloor in my bathroom and installed 1/4" hardibacker using thinset and the correct backerboard screws, my floor still seems a little uneven, around 1/8 of play maybe a little more. I guess its easy to spot as I plan on laying 24"x12" tiles and they dont sit flush on a dry test. Will they be ok once I bed them in thinset or do I need to apply some self leveller first. This is my first attempt at tiling a floor, I have also installed an underfloor heating mat which covers approx 1/2 my rooms square footage.