Hey guys,
Never heard of adding nocking to the center improved arrow speed (which makes sense, anything on the center of the bowstring will reduce arrow speed, be it a heavier arrow, heavier/thicker serving or multiple nocking points) BUT I competed a lot with the compound and I know for sure that a couple nocking points on the END of the string, about two inches from the pulleys, did add a few fps. I dont think such a fix would improve speed on a selfbow.
cheers
Matthieu