better yet, just put the top of the nock point even with shooting shelf. This way your arrow will be above the nock, and it allows you to shoot different diameter shafts without having to compensate on the nock end of the arrow.
This is also how Howard Hill used to place his nock point. He said it made it easier to shoot faster. Claimed it was faster to clip on arrow and slide down, instead of clipping on and sliding up. It all sounded logical to me, so that is now how I place mine. Top of nock even with top of shelf.