It's not uncommon at all for long, high BC bullets to moa better at longer ranges.
Right, exactly, when you're measuring angles, not absolute group size. I had a Sendero in 7mm STW that shot 3/4 inch groups at both 100 and 200 yards. It would also shoot 3/4 MOA groups, in other words, 4 inch groups, at 600 yards. There was some wonky wobble for a short distance downrange.
If someone is getting smaller groups, in inches, not angles, at longer distance, I'd suspect parallax or some other source of user-induced aiming error.
Tom