If your pin is set to twenty, it will of course be low at 30 due to arrow drop. It will also always be low at 10, because of the trajectory of your sight in relation to the traj. of your arrow. Think of it this way; if you draw an imaginary line from your arrow to the target, and an imaginary line from your eye through your sight, to the target, those two lines will only touch at your set 20 yards. at ten yards the arrow line is below the sight line. I'm not sure it should be exactly 5 inches, but it should be low.
-jake