If you are a little nock-high or not quite tuned, the position of the broadhead will make a difference. The not-perfectly-tuned broadhead will catch air even on a non-windy day, based on which way that "wing" (broadhead) is facing. Just like a kite that floats on wind resistance or falls like a rock without it.
The trick, in my limited experience, has been that if a broadhead doesn't fly straight, I can start heating up the insert and rotating it from 12 to 1 to 2, etc. The timing of the rotation of the arrow at the time of the strongest oscillations -- before the feathers straighten it out - will affect the arrow's flight. At some point on the clock, that head should encounter the least planing effect.
In a perfect world, an arrow should fly perfectly and this shouldn't matter. But I'm having a tough time getting a bareshaft tuned perfect without some nock-high. Evidently, it's due to my release. When shooting some Zwickeys with my best-tuned set up, they were not flying consistently. After I spent an hour shooting one, rotating the head, and re-shooting, I found their sweet spot. I then rotated them all to match, and get good flight out of them.
Archie