I'm trying to figure out the best way to level out my old bathroom floor and at the same time prepare it for bathtub placement and tiling. The entire bathroom is about 8x5 feet and from the back left corner to the front door it slopes 1 and 3/8ths of an inch. I can only heighten the floor a maximum of ¾ of an inch (including tile height) to match the existing maple flooring in the next room and to come to the bottom of the cast iron toilet flange so I won’t be able to completely remove the slope but I thought I could level it out a little. To level out the entire room would you use asphalt shingles sandwiched between the plywood subfloor and 1/4 inch backer board (permabase)? Or would you just recommend pouring floor leveling compound over the plywood subfloor (prior to the pour I’ll use the primer and I’ll staple hexagonal wire on top of the subfloor per manufacturers directions) then applying hydraflex over the leveling compound to prepare it for the tile and tub.