RE: Offset Vanes/Feathers on Crossbows
That came up in a discussion I had a few years back with one of the co-owners of Horton. He recommended not using straight fletch and going with 2 degrees of offset. I'd would recommend going with as much as possible without getting contact. Those things need all the help they can get in the accuracy department.
Cool thing about crossbows is that you can brace on a sandbag or in a gunvise to check for improvements while eliminating some of the "shooter error". Try some different things and tell us what works best for you.
What type of crossbow are you using now? Good luck this season!
-Chief