IMO shooting off the shelf puts the shaft of the arrow closer to your hand making instinctive shooting more accurate. Being closer to your hand means you don't have to mentally adjust to the 1/2" or so above your hand. (For me, when compounds came out, I tried shooting a one off the shelf with fingers and it was almost impossible after shooting for decades off the shelf with a recurve) .If you have arrows that are properly spined your fletching will not contact the riser of the bow. The arrow shaft flexes upon release (archer's paradox). The amount of flexing can be manipulated somewhat with the weight of the tip. A heavier tip will cause more flexing than a lighter one. It should be noted that an arrow will always flex whether your shooting with fingers or a release. With fingers the arrow will flex side to side. But with a release it will flex up and down.
Here is a simplistic explanatory video of archer's paradox: https://www.sciencealert.com/watch-t...in-slow-motion