Sch, I found your comments very interesting. I've had a few DF's and bents try to pull in and draft with me with my fairing, one a jet pilot who tried it and said it was like trying to follow a 747 with its massive wake turbulence! He's an experienced biker and he couldn't do it. So I think you are correct with your analysis of the air flow.
If I'm not planning on going very far or very fast I put the fairing cover over it and wrap it with a few soft bungees and it travels OK. But for any longer distances its better to take it off.