I shoot with all those cants too (vertical, horizontal, upsidedown and everywhere between), and also using perfect form and tuned equipment, Terry, as an instinctive shooter, i think you don't actually realize the left-right adjustments you make instinctively to accomplish these shots. However, us split vision and gappers must visually make the same adjustment, that you just make instinctively.
A perfectly tuned bow with the arrow nock coming out of your pupil would indeed eliminate the necessity for adjustment, but the best we can get to the nock coming out of our pupil is having it postioned below it, by about 2". So we are faced with a problem similar to canting a scoped rifle. The arrow must travel upward to meet our line of sight (or sideways, with a horizontal bow, at which case, the arrow no longer has gravity to slow its rise, and this lack causes the arrow to move left/right signifantly). It's exactly the same phenomenon as canting a scoped rifle, the way the nock is positioned 2" below our eye:
Yosemite Sam discusses this on the form board
https://www.tradgang.com/tgsmf/index.php?topic=113849.0