I have found that I can shoot 4" soft vanes with a slight RW helical if the arrow is placed cock feather in. This works even off of the narrow shelf of my Hill style longbow and no sweat at all from my '72 Kodiak Mag. These are all on shafts that otherwise shoot very well with 5" feathers with a bit more helical, and both setups with broadheads.
I know it's not "trad", but I've been shooting vanes of one sort or another since '66, so I guess it's sort of traditional for me, at least. I prefer feathers, but with the forecast combination of El Nino and the new La Nina this fall, some form of waterproof fletching will be needed from time to time.