1/2" would be a little low for me for 3 under. You might want to try 5/8".
If your bareshafts flew well, but your fletched arrows have a bounce, it could be feather or quill contact with the shelf or riser. Moving the nock point up could also help eliminate this. Also, if the arrows are too stiff, you can get a bounce from feather or quill contact with the riser.
You could try trimming the feathers down to the quill on one of your arrows, and then dabbing lipstick or something on the quills next to the shelf and riser, and then observing if any lipstick is rubbing off on the shelf or riser when you shoot the bow. If so, you can try rotating your nocks a little to get clearance, or trying a slightly weaker arrow if you're getting riser contact.