Yeah some of them are a tiny TINY bit taller than others.. I had the same issue that you had, and I just recently redid the way I placed the workshop and it seems to be good to go now. So set the track up and let it autolevel the ground. Then, raise the ground where the workshop goes to about 3/4 of the way up the rails (so that the rails are barely showing above the ground) then place the workshop. This places the workshop a little bit higher, and still shows the rails thru the concrete floor. Let me know if that works for you? It seems to be working for me so far!