this^^^
if you sight it in at 10 yards, you are starting with a lower angle than if you were to sight it in at 20.
if you sight in at 20, your starting (launch) angle will be slightly higher to bullseye at 20. It will not be much higher at 10 yards, so there should be very little difference.
but if you are starting the launch angle low to zero at 10, the arrow's arc will be so flat that you'll be much lower at 20 than you would be high at 10 if you were to sight in at 20. make sense?
it's the same with rifles.
so lets take a 7mag, 140gr bullet, muzzle vel of 3150 fps.
zero at 100y:
-2.5" at 200, and
-9.6 at 300y.
now lets zero at 200...
+1.2" at 100y
-5.9" at 300y.
you see the difference?