RE: arrows impacting dead on at 20 yards and almost a foot left at 30.
I would have to agree with rest of the people here that it may be a torque issue. I shoot with a string that is intentionally to short to avoid any chances of string slap. Obviously, this creates torque on the bow. The only thing that improved my accuracy at allranges and allowed me to see the torque being applied to the bow was a sight designed for that application, such as the Dusk Devil sights. It improved my shooting form, allowed me to correctfor thetorque my hand was creating on the bow and made me follow through to arrow impact. For me it was a form issue due to the short draw length, but it was corrected by the sight.
Hope this helps. Good luck.