If you are too close to the nock you may make contact with the vanes when you anchor. If you are too far away from the nock, you could affect the FOC (forward of center) of the arrow. That being said, I clamp the vane so the rear of the vane is even with where the marks on the Bitz jig start. It winds up being probably 5/8" from the end of the arrow (not counting the nock). I'm not an expert by any means, but that's how I've always done it.
