There's a video floating round here somewhere that I posted of us riding beside larry on the 4 lane between Decatur and Huntsville. We were running 65mph or so and both the flags he had mounted at the back of his rear deck were flying toward the cockpit. Proof of the huge backdraft toward the cockpit of the Sling from the rear. There are as many solutions as there are different setups. Each one is different and requires a different approach.
I remember that picture. Early on riding behind Bubblehead his two flags were flying sideways, I think that was right after he installed the top.