As Big country stated in the other thread,the answer is simple geometry.Of course it is much easier to show someone than explain it in words.The best that I can do is to suggest that you look at a drawing of a bullets trajectory in relation to the line of sight.You will seethe line of sight originating from the sights or scope,and the bullet path originating from the bore.Now look where these lines cross,usually at two pointson the drawing.Now imagine that the line of sight started from further from the bore.If it still meets the bullet pathat the same firstpoint on the trajectory curve,will it still cross the bullet path at the same point the second time?The answer is no,since the angle between the line of sight and bullet path is now different,the second crossing will be at a different point as well.