I have had the new owner shoulder the unfinished rifle with the front sight on ,but without the rear sight installed. I then stick the rear sight on the barrel temporarily and have them sight a target wearing the glasses, if any, they use for shooting. Then avoiding the hand carry area, I move it around. Younger eyes prefer closer to the eye, older further. I have even moved rear sights foreword for aging shooters. It also is a good time to check if the cheekpiece is too high if you use a rear sight low enough to duplicate one in the dovetail.
IHS, Turtle