You have stretched the threads if you feel the screw stop turning and then tighten it some more and feel it give. Do not get thread lock on plastic parts. Thread lock will attack most plastics used in sights. The pin gap increases with the distance from your eye. Pin gap will also get greater at longer distances because the arrow will fall faster as it slows.
Some sights have pins that actually touch.
That can be a disadvantage because the target is obscured by the sight pins. The target is what you are aiming at and need to see. You can t hit it if you can t see it. That is why most target shooters use one movable pin. You can move your sight further out or change your sight distances.