For my woodies I use to use 5.5” fletching, then I went to 5” and now I’m using 4” shields. Seems to steer the broadheads very well and less noise.I've been doing just that. It helped me realize my 4 inch cut shield cut with a helical twist are much more forgiving of a bad release than my 4 inch straight fletched parabolics. They both guide an arrow just fine when I execute the shot perfectly l, but I'm going with the arrows that still fly good when things are less than perfect.
All I shoot is 2 and 3 inch feathers. Never found a need for more then a 3 inch honestly, as long as the bareshafts are a touch weak, dead laser, or even a touch stiff not much feather is required to get broadheads to group with field tips.I now shoot the 3" feathers after shooting 4" for awhile. If the bow is tuned, they fly great with BH's.
Yuk.....Those 5" feathers are like a Flu flu...they drop like a rock out past 30y or so...