Then how do you explain setting one up with a level and a square? If it's perpendicular/plumb to the string......it's Perpendicular/plumb to the ground. If you're using a bubble level to set your arrow......what's it "level" to?
The bow/arrow is set up at level/plumb/center in a vice, not when your holding it. That is designed for the arrow to come out of the bow as straight as possible. Then you pick up the bow, and your raising it to shoot down range.
Think about this Jeff, when you shoot 40 yards, do you not raise your bow? If you were to shoot 60 yards, do you not raise your bow higher? If you put your bow in a shooting machine, plumbed and leveled it so the arrow is level and shot it, it would not make the spot on the 20 yard target. It would not arch up, it would come straight out of the bow and start to drop immediately.
When your shooting 20 yards, your not holding the arrow level, your bow is level side to side not front to back.