I remember learning about height over bore back in about '97 or so, shooting 3D archery tournaments. Occasionally there would be a target at about three yards, and to hit the kill zone I would have to set my sight on about 40 yards.
I learned this shooting an indoor league, watching one really good shooter practicing beforehand standing right in front of the target bale. I was curious what he was doing, so I asked him.
He told me to stand where he did, and try to put an arrow into the same hole he did. My first shot was way low. Then he explained the concept.
It was quite eye opening, to say the least. Then it was fun watching a lot of other archers miss the kill zone low on the three yard target that night.