cool, thanks for the reply and info.
So intheory if I mounted them say 5mm short of maximum extension, and then dropped a shell size (10mm?), technically I should have room to adjust for this size difference.
I don't think i'd risk doing that, but in theory I assume that would work.
Current boots are 318mm bsl, new i'm debating buying are 305mm.
Looks like I won't be able to mount to accomodate both of these boots huh