I think to a degree you absolutely correct. Just because they are downwind doesn't mean the are......downwind. Like you said, the thermals have a lot to do with it, also the wind currents downrange of your stand. For example, I was sitting in natural ground blind watching a clover field. The wind was hitting me directly in the face for a while, then turned and hit me in the back of the head. So, I got up to move across the field, but when I hit the field edge, the wind was blowing from my left to right......So I sat back down and gave a couple puffs........Sure enough, that cloud went right to the edge of the field, then turned to the right and blew in a good direction. It was a learning experience for sure, and I saw several deer that were easily in range that night. Unalarmed and with no idea I was there. Thermals and currents are very interesting, and something I now think about much more.

I also had a doe that I knew was downwind of me one evening. So I puffed a couple, and that cloud hit her right in the face. Can't be more downwind than that, and she fed on clover for half an hour, totally unalarmed.