I'd almost bet it's your high nocking point that is allowing you to shoot those arrows well.
Several years ago there was a fella building really fast bows named Bill Matlock. His bows were called Predator bows or Matlock Predator but I don't believe he's around any more and the current Predator bow company may or may not be anything related.
Anyway, he was a bit like O.L. Adcock in that he did a lot of testing to squeak out a couple of fps here, a couple there and pretty soon had some real fast bows. Very knowledgable fella. He came to the United Bowhunters of Missouri Rendezvous several times and one year put on a seminar about bow tuning. The main thing I recall was that he stressed starting real high with your nock point and working down when tuning rather than starting low and working up like most people. He'd start at about an inch or more high and often got great flight long before you would think possible. In fact, he got such good flight with high nock points he started to experiment with various spines from multiple bows and found that for some reason a nock point of around 3/4" to 1" was very forgiving of spine. In his demo, he shot the same arrow out of bows from about 35# to 65# and showed good flght and accuracy.
Personally, I've always stayed around 1/2" to 9/16" but I always remembered Bill and his high nock points. This was close to 10 years ago or so. I'm not certain but I don't know if he's still alive. I believe I recall something about him being in bad health not long after and I never hear about his bows any more.