I am thinking that, hypothetically now... for a short time, maybe two to three feet from the time the arrow leaves the string, it is not spinning. At that time, it COULD also be going thru paradox, that is, waving back and forth. If you have seen a high speed video of arrows in action, you know what I mean. If it is vertical, it COULD catch more air and move the head one way or another. If it is horizontal it PROBABLY WON'T catch more air, although the videos also show some up and down motion too.
Once it starts spinning, all of that stops mattering. I think.
Does it matter in the real world. I don't know. Probably not since a lot of you mount them verically and geet good flight. I mount mine horizontally ...and get good flight.
Something to talk about.
ChuckC