One of the advantages of a cocking-piece peep sight is that, as soon as you pull the trigger, the sight springs away from your eye before the firing pin actually touches the primer. The distance you should consider is that from the eye to the sight in the fired position. As for free play affecting accuracy, the cocking-piece peep is not a precision competition sight; it's a short- or medium-range field sight, often on moving targets. It's more in the same class as the battle apertures used on P14's or Garands. Better quality construction can just give you a bonus in accuracy.