I have similar results myself over the years and have wondered if it was just me or everyone else has the same issue. There's only a few times that I have saw anything and when I did they moved quick through field or moved through on a brisk walk not stopping for anything. Now if I see the wind will be sustained that high I don't go out. Just my opinion though. On Flip side to your question do you experience little movement on cold clear mornings no wind. Seems to me when it should be perfect conditions I don't see much.