Hi! I love glass tile. It really depends on the design. Sometimes I will use a pencil or liner between the two, which separates the different tiles and makes that difference ok. If we I am not using a pencil/liner, we will just float the thinner tile out with a little more mastic. That is not always the easiest solution, but it has worked for us in the past.

Thank you, I will check out a pencil and liner, since the thinner tile is thicker.