grahamster

im tiling a hallway for a customer jst now and they have asked me to level their living room floor for them.so they can put solid wood flooring down.It is a concrete floor and is about 20msq,however from the middle of the room to the wall the floor tapers off from 0-12mm.what im wanting to know is can i fill about 7-8mm with rapid set and then go over with multibase self leveler to try and keep cost down,or does it have to be leveler all the way.......cheers graham