I get my bow strings from Chad, he gets the serving to be just the right thickness for the 5/16" Mecury nocks. If one has the string nock above and changes from a narrow 1918 aluminum to a parallel 11/32" or 23/64" cedar your arrow position will be pushed lower relative to the arrow rest. With just one under the arrow any change in arrow thickness will not matter. The arrow, if the nock is loose on the bowstring, will have a greater chance of sliding down the bowstring than up on release with an ASL. Some prefer to slide down towards the nock when quickly putting an arrow on the string without looking. I suppose I do this a little bit, but i do not pull the nock tight into the string until it is in position, which I can feel with the side of my thumb. The initial beginning of the throat of the nock does the sliding down, not the complete throat of the nock. On some strings I do have a small nock above. that is for simply keeping the arrow on the string if I am using a nock that has a little bit looser fit while still hunting. Yes, I walk around with an arrow on the string at times, when it is safe to do so. When I am rabbit or pheasant hunting, way more fun than sitting in a tree stand, I almost always have an arrow on the string.