First of all, forget about this bare shaft stuff. Measure your centershot at 13/16", and make sure that idler wheel is dead nuts straight with the string feeding off it when at full draw. Idler wheel position may change from static to full draw, but only worry about it being straight at full draw. That idler wheel affects things way more than a lot of people realize.........make sure you fix this immediately.

Once this is done, I would then start looking at arrows. First of all a 340 is WAY to stiff for a 28" - 70lb Marquis..........even with a 125 grain head. With 100 grain inserts and 100 grain heads, it's underspined. If it were me, I would be using a 400 with a 100 grain head, and drop the peak weight down to 68lbs. That should spine perfect out of that bow, and that's the combo I would be trying to tune the bow for.

My Marquis tuned perfectly for both walkback and paper using an arrow spined correctly in OT2, and at 13/16". I'm drawing it at 30.25" AMO. If there were issues being created by torque from the roller guard, it would only be magnified at my DL, and it's not. I would try the above suggestions and then see what it does. I'm willing to bet a combination of idler lean and improper spine are causing your issues.