Very interesting... tried taking a few shots with the top limb turned out a bit (.5-1.5 turns). This produced the same tail high impact but now I've got a nice scar down the length of a bareshaft arrow. It basically starts an inch behind where the arrow sits on my biscuit at full draw and runs down the entire shaft.
I never even thought of looking at the end of the shafts to see if there were contact marks until I saw how badly this one was scraped. Went back and looked at the other bareshaft and it has the scrapes on it too (did not use this one for the limb test above). Then I looked at the fletched arrows and they have the same markings at the front (an inch behind where it sits in the biscuit at full draw) but almost no marking toward the tail end.
As a follow-on test, I took that same scarred bareshaft, flipped the nock over, and shot it again. Sure enough, it has a nice little scrape down the other side now too. Seems it is hitting somewhere on the lower lefthand side (I'm a lefty).