I have a laundry room I am getting ready to tile but my floor is roughly a 1/2 inch lower in the one corner. Some have said to layer the leveling compound to achieve the build up needed but others have said just to use thinset underneath the cement board. Can I build up thinset that thick? I also was told that screwing down the cement boards through leveling compound will just crack it. What would be the best way to do this right so my tiles don't crack in the future?