Once fireformed to your chamber, the brass will headspace off of the newly formed shoulder. At this point, you shouldn't need to full-length resize for a very long time, perhaps never. So your only sizing concern at this point would be sizing your neck to provide some tension on whatever sized bullet fits your bore. I got lucky with mine....so I can basically hand-seat a .446 boolit in a fired case without sizing at all. I then add a slight roll-crimp (of sorts) using the bevel at the bottom of a 44mag sizing die. It just happened to be the right diameter for the brass to catch the bevel and not actually enter the die, so the angle of the bevel slightly forces the neck into the crimp groove. Some of the boolits will spin in the neck, with a bit of effort, but I've never had one push out of neck from compression.
Does this help? I might have just confused myself??