I don't mean to drag this out any more, but here is how I "teach" new shooters how this works.
Lets say you have a lazer beam....a strong one. Lets aim your beam to be dead on at 100 yards. your lazer burns a hole through your target. lets put another target at 200 yards, and 300, all the way out to 1000 yards so that the beam burns a hole dead on the "X". Now you have 10 targets with a hole burnt center X....
Now, lets tilt the the laser so it is 1 inch high at 100. it burns through and hits the 200 yard target. Now the laser does not bend...it goes dead strait. The hole on the 200 yard target is 2 inches above the x. At 300 it is 3 inches ect...all the way to 1000, where the laser is burning a hole 10 inches high.
Now, lets pretend that 1 moa and 1 inch are exatly the same at 100 yards. They are VERY close, but not exact. We moved the lazer 1 inch at 100 yards. Now since an inch and an MOA are the same (in our little experament) we can also say we moved our aim point 1 moa at 100 yards. But, as we look at our 1K target, it moved 10 inches, and at 700 yard it moved 7 inches, and 5 inches at 500, even though we only moved the Laser (cross hairs) 1 inch, or moa (at 100). So 1 moa is 1 inch at 100, 7 inches at 700, and 10 inches at 1000.
Now, let reverse this....lets say that the balistic chart says that your bullet will be exactly 200 INCHES low at 1000 yards with a 100 yard zero. We know that 10 inches at 1000 yards was the same as 1 inch, or moa, at 100 yards. Rember the lazer. Now, doing a little math in our head we know that if 10 inches at 1000 = 1 inch at 100, then 200 inches at 1000 would be the same as moving 20 inches (or MOA)at 100. (just divide by 10) So the "come ups" to hit dead on a 1000 yards is 20 MOA (or equal to 20 inches at 100 yards) to raise the bullet impact 200 inches on the 1000 yard target..
If you are working at 600 yards then divide by 6......400 yards, divide by 4...ect... to turn your inches into MOA.
God, as I read this it sounds so bone headed.....kinda hard to put on paper...but on the range it helps people understand.
Good luck