RE: "Margin for error"
The black dots on my yellowjacket bag are approx. 1 inch diameter. I aim for a different dot on each shot. If my arrow is not at least touching the black dot on every shot, then "I" did something wrong. This is the way I practice regardless of distance. Obviously, I'm not yet able to accomplish this on every shot at every distance. I guess this means that my margin for error is 1/2 inch.