But with tile it would depend on the thickness of the tile. I have installed tile flooring for some time in the North East and for this I use the plywood subflooring and a mortar bed. It's a little more work, but you'll never have to go back to work on it again. The concept is simple. By installing a mortar bed, you'll get the proper adhesion with the tile.
I have used cement board as well as the plywood.
What type of mix are you using on this tile to adhere it to the floor?
Your local tile center should be able to help with this.