I've mostly hunted with longbows shooting split finger while using a backquiver. For the first twenty years or so, I nocked the arrow onto the string below the nocking point. Around the last ten years I switched to nocking the arrow above the nock point. I now agree with Hill as I find nocking the arrow from above to be the smoothest and most natural way to get an arrow from the backquiver onto the string. Even when using a low opening side quiver, nocking the arrow from above is more fluid with less motion.
Coming over your shoulder with the arrow nock held between your finger(s) and thumb, straight down onto the string is near fool-proof as your thumb brushes the nock point on the way down which eliminates fumbling. Nocking from underneath requires you to come down past the nock point then change directions in movement which increases the chance of fumbling. When hunting small game, winged game, following up on wild boar, bear, etc., such fumbling will often rear its ugly head and cost you a shot. A vetted archer who can quickly and smoothly nock the arrow will have a huge advantage and will more often make the shot and bag the game.