One other thing to say, the floor levelor will aid only in making a smooth transition between two sections and something to glue to.
I have always been told that the expansion and contraction should and will occurr between the underlayment and the walls. This is why the underlayment should not be tight up against the walls. Just like on hardwood flooring, you do not butt up to the walls. You leave a 1/4 or more of space for movement then the shoe/quarter round molding cover up the space.
Here in Texas, like many other places, our earth and foundations are in constant flux of movement. During months of no rain then fall and bow, during wet months they contract and swell up. This space allows for that.