wind break -- The South wind blew over the top/around the board which drew the fire/heat/smoke back towards it
I find the funnel action you describe hard to predict, so I shy away from using wind breaks altogether: instead I add more wood for incresed heat to counter the wind's cooling effect.
My set up has the additional horizontal choice of adjustment so I can place the food directly in the path of the heat no matter what direction the heat/wind may choose to do.
Nother question: When I read you posts, I notice that you more often than not picture a very low key fire. How long is the typical cooking time for the type of things you do in your pictures?