Another and i think better way would be to use a self leveling concrete that can be aplied in a much thinner coat and if head room is a problem would be of help.
Cement over tile floor.
Examples of fiber cement board.
Mainly the products i m talking about are considered to be cement backer boards for tile installation.
Cement board and fiber cement board.
Examples of cement board are.
If you were to use conventional concrete i would say you should pour a minimun of 3 inches both for strength and to ease leveling.
Lightweight cement based overlays mimic stone brick and other wall textures placing overlays over tile floors by chris sullivan chemsystems inc.
These come in two categories.