And blow that sucker right off?
My thought experiment is to start with a complete boat-tail (my spell checker likes it hyphenated, sorry). Obviously, at full length, it ends in a round pipe. But as you truncate to make a place for legal niceties like license and tail lights, it seems the air exiting is adding to the bulk of the moving air whether it's relatively higher or lower pressure, so at the outer edge wouldn't it shed a non-turbulent curtain off the end — extending it virtually. Compared to just dumping it into the middle.