[hat_man]

The angle trim doesn't support the undertray just attaches to it. I was thinking like the prow of a boat. Something to just help redirect a small portion of the air outwards. My thought was, if you could move some of the air out and away from the big ugly "parachute effect" area at the rear, there might be a small advantage. Nowhere near perfect, but every little bit helps, right?

With the picture being at an angle and just finishing a couple of "pork chops in a can" my fairly weak MS Paint skills are pretty much shot on this one, but maybe this helps?

The dotted lines only represent the idea if someone had an undertray that extended further back to say behind the rear wheels, but no farther. Green for the extended tray, blue for the extended angle trim. I guess if a person had a full undertray, they could put the trim all the way back to just in front of the rear wheels?