Are you 6-8 inches shy due to running out of furling line or just unable to furl it all in?
Are you keeping the same level of resistance on the outhaul while furling the main?
I had a 331 and can't say I had that problem on the main as I was extra careful about the outhaul resistance to keep creases out of the main but had seen it on my jib when furled too loose, too sloppy on my part.
Furling line is plenty long. This just started happening. Seems I solved it yesterday during the holiday weekend here in Chicago. While the main was fully outhauled I released the boom vang and topping lift as well as a little slack in the mainsheet. This resetablished a "natural" set of the main.
Anyway when I pulled the inhaul in the main fulrls up nice and smooth and even and went all the way in to the black line that shows your up to the UV panel.
Did this several times and worked well. Also seemed like less muscle required.
I summary I feel the foot of the sail and the leech are at equal tensions which enable it to roll nice and easy and flat. I think before I had some relative slack in the foot which bunched up.
Anyway thanks for your input.