Hmm, this is why I never really like the GCFX mask, much too big IMO. The only way I can think of to resize it is to cut and remove material from certain places. Namely, the side pieces and top "brace." This would make it a tighter fit, but I do not know if you want to go this route as you would lose some detail. Honestly, that is what I would do and use it as an excuse to revamp other aspects of the mask as well.