Agree 100% with the thermal analogy. In the evenings as the sun goes down, the humidity in the air will begin to settle back toward the ground. This is what gives us dew, frost etc. Those does may not have busted you due to there still being an updraft in the air thermals. the wind may have been blowing their way, but the updrafting thermals kept your scent above them at ground level.
As the evening progresses, temperatures fall and the humidity settles, taking any scent that you may be shelling out with it.
Happens to all of us..