I used Chairgun to figure this out. Using Crosman Premier lites, 850fps and the scope height of 1.75 in. If your 1st zero is 13 yards you'd be .85 inches high at 30 yards and dead on again at 45 yards. Of course you'd want to actually verify this by shooting your pellets at the distance to account for any variables. Usually Chairgun is pretty close though.
HTH
Nathan