If you notice your fire box you will see the air that gets into there goes through the cast iron 'dran hole cover' the only thing that would caust that air to go back to the back of the egg would be the way lump is stacked. The other air inlets are up higher in the fire box (below the fire ring).

The other thing you may want to look at is where you start the fire in the egg, front, back, sides, or more than one spot.

I try to start my fire a little to the front of dead center or two starts, left and right of dead center. I notice the corn husks getting 'more burnt' on either side of dead center.