When I designed the adjustable headstay assembly, I used the max back (34' 9") as my 7/8 point. From there, we were able to pull it forward roughly 2.75", I think. A lot depended on the tools we were using and wherever the rig started at (ie. pigtail length and length between swivel and halyard block). Most riggers use a 2/3 rule for making wire lengths with adjustable turnbuckles.
As for jibs remaining furled over time, I don't recommend it because it can lead to a permanent curl in the patches and along the leech. All things that will make you cringe when trying to sail in light air. Not to mention that having a jibsock on there flapping in the wind and vibrating the rig will only lead to excessive mast/rigging wear.
