backerboard over leveling compound

I am remodeling a half bath and have a problem that the floor has a hump in it. The room is 63" x 72" with the high spot near the center and a 1/8 to 1/4 inch drop nearly all the way around the walls. I have sanded the hump down to this level (it was higher) and do not want to thin the plywood more. I have read the threads on self leveling compounds and durarock like applications but my question is can you use durarock over the self leveling compound. When I drive the screws through the durarock through the compound into the subfloor will it mushroom the compound underneath such that you have stress concentrations and thus cracks in the future. I want to put tile over this. Any help or suggestions would be welcome.
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You have to thinset the backerboard ( durock) to the floor.( plywood subfloor) I use a 3/8" by 3/8" trowel. I do not use screws I use 1 1/4" roofing nails the thinset will hold it down. You can also use the thinset to level the floor While installing the tiles
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plywood. You only need screw/nails in a few places to keep it from sliding around as you work on the next sheet. I find it is less messy to level the durarock first (Thinset under it) rather than trying to level the finished tile install. Either way will work.
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Thanks for the advice. I will use thinset under the durock as you suggest.
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