This is a 8 x 5 bathroom floor on the second level. The wood subfloor seems to be in good condition, no movement, solid. One section all of the old thin set that came up very nicely. The rest of it was a bear and I could not get it up at all whatsoever and seemed to possibly have something like self leveler over the thinset. We already primed it with the intent of putting floor leveler on it but am having second thoughts. I believe the largest variance from the lowest part to the highest part maybe a quarter inch. we realize that the floor leveler will be pretty thick in some areas. Is there a reason this is not recommended? We intend on putting down a heat mat, thinset finishing with large 18 x 36 ceramic floor tiles. Thank you.