I would tend to agree a panel sitting up higher would catch more wind. The one advantage with the panel sitting up higher is they are basically floating in the air. If the wind is blowing on the panel, it will just keep blowing underneath it out the other side.
With a factory install a heavy cross wind will get stuck under the 4" inches of panel and hit the mounting bracket and create an area of high pressure. With the free flowing air on top of the panel, you get a low pressure. Thus creating a lifting action on the panel. (This is how airplanes fly)
I did not see both panels come off. But the AC unit wasn't hit either time. Again suggesting the panel was ripped off from the side in a cross wind type situation described above.
2009 Chevy Silverado
2011 19' Escape