Another reason for gluing a thick piece of leather to the shelf is that sometimes the bow will not tune with just a piece of Velcro or something similar on the shelf. I have had this happen at times with bows that have a threaded hole for an elevated rest, like my Satori, but not with bows with no mounting hole. I suspect that some bows were designed to be shot with an elevated rest, while other bows were designed to be shot off the shelf. Some, but not all of the bows that I suspect were designed to be shot off an elevated rest have a persistent nock high, and the only way I have found to get rid of it is to build up the rest to where it is closer to the height of the mounting hole.