Wingbone

I have found that shooting off the shelf makes it easier to shoot instinctive accurately. It puts the arrow right above your knuckle. Shooting becomes more like pointing your index finger. When shot off a shelf, feather fletching will collapse as it crosses the shelf. Plastic vanes won't do that and thus will kick out the back end of the arrow on the way out. That messes with your arrow flight.
I shot off the shelf of my recurve for over 30 years with perfect arrow flight. I glued a paper match stick-sized piece of leather onto the shelf at the high point leaving a slight gap between it and the riser. Over that I placed a patch of self-adhesive velcro (the fuzzy side). On the riser adjacent, I glued a patch of buckskin. This setup gives a single silent contact point for the arrow and the small gap allows the hen feather vane to pass through without disrupting the arrow flight. The velcro wears after a while. I'd just pull it off and replace with another patch.
Bowguy is correct, you'll need to adjust your nocking point higher than you think to get good arrow flight off your shelf. I think I had mine set about 3/8 in. or so above plumb.