Well as long as the half size up is snug and as long as you are happy with it then that's all that matters. But remember that the liner will "pack out" after several days of riding, so if it has room around your foot now when they're new, then they will be even roomier after a week or two of riding. If Burtons run small you should be ok, or you can always add a foot bed insert and that will take up some of the extra room
The half size up is snug, but my toes are still able to move around. When wearing boots, are toes supposed to have wiggle room? How big is the "pack out" is it a small change like half a size? (I have the Impact 3 liner from Burton).