Yeah, a L/XL will def fit on a 25.5. But maybe not anything smaller. Since a L/Xl will accomodate a boot as small as 9.5 it will no doubt work with your size 10.5 with shrink tech.
I was just saying, because I ride boards 25.5 and and narrower I prefer going with the M/L, which you could probably do as well. Either way, you're fine.