Jeff, if your at full draw and aiming at a 20 yard target your arrow will not be level to earth, it will be point high/nock low. Your arrow does not leave the bow level when shooting at targets down range, remember the arch,
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. Ifyou're using a bubble level to set your arrow......what's it "level" to?
Also......This has nothing to do with the original question......but wouldn't the location of the target at 20 yds determine whther or not your arrow was "level" with the 20yd spot? Or....are you saying that ther eis nowhere you could put your target and have your arrow be "level"?