What about the bayonet's loop that goes around the muzzle, centered on the barrel axis? A lug under the BM59 gas cylinder would be further off-axis than the lug on a 1903 or Garand.
Sometimes guys who work requirements get stuck on little details like that and lose sight of the bigger picture during development programs. Just look at what the Army Air Corps did to the high-performance Bell XP-39 prototype that turned it into the dog that was the P-39. Some AAC requirements guy at Wright Field got fixated on coefficient of drag, and, voila, no external air scoops for turbo-supercharger or intercooler were allowed in the final design because they created drag, even though removing those features significantly reduced engine output, especially at higher altitudes.