[joetapley]

"The zero position for the fletched shaft was the centre of the target face Omm O degree determined by moving the entire assembly "

Maybe I'm being dense but this 285 degrees - it means the the bareshaft was hitting to right of the fletched shaft at whatever distance?

. I agree entirely that the two arrow configureations behave in adifferent ways , But my question is... why set up the bow to arrow A, and then in competition shoot arrow B that you know to be different?.

You are essentially adjusting to a null position. Although the two arrows behave differently you are looking for the setting at which the difference between the two arrows is a minimum. Same approach as speed tuning, your finding the setting at which the speed difference between the fletched and bareshaft arrows is a minimum.