Thanks for the info.
A phantom tail, that's a good way to put it. So I guess the curved surfaces at the rear help the air 'make the corner(s)' at the rear and meet up, theoretically, at the point where the four planes would converge if the tail were complete?
If this works I may try the belly pan if I can find the right materials. Do you have any idea how to 'treat' the dually rear wheels? There's got to be some crazy things going on there as the air goes over, around and through the tires.
Should there be some kind of diverter in front of the tire sets to help direct the airflow? How about behind the tire sets?
What kind of improvements did you realize with the Prius 'tadpole' tail?