I think I owe you an apology. I pulled two pair of my XT17's apart today to dry em out and everything is marked with a single size - 28.5 in my case. The shells have the uni-size molded in. I have 3 extra pair on the shelf and even the box labels are identified with a single size. So, the XT17 may be sized in .5 increments.
Maybe L7 or one of the other boot gurus can tell you for sure.
Please repeat after me...No Major Manufacturer Makes 1/2 size ski boot increments...No Major manufacturer makes 1/2 size ski boot increments. The XT is sized on the .5 meaning there is a 26.5 a 27.5 a 28.5 (no full sizes). I know this gets confusing but it get simpler if you understand that the nobody makes 1/2 size changes in ski boots. At any level. Ever. They don't change the liner or the boot board, the footbed is slightly thinner in the .5 thats all that distinguishes a 1/2 size and that crappy POS should be disposed of and replaced with at least a trim to fit footbed immediatly.