Our arch enemy: The side mirror!
 

MetroMPG shared that post about the Bonneville Fusion and one detail caught my attention:

That was something that I had not understood.

So, some mirrors have aerodynamic fronts, but the backs ruin everything, despite having a sharp trailing edge. From what I understand, you want the trailing edge to be no more than ten degrees below the roof line.

What if you extend the bottom edge of the mirror to the back of the window or the door? A 4" tall mirror that extends 22.685" would form a 10° angle with the top and you might not be able to see the extension if you also taper it in 10°

Would that do any good?

Mirrors are a overlooked economy offender and has a lot of room for improvements.
I think having a custom smaller mirror in place would be of more benefit. If you put a smaller mirror on it say 3 inches high mounted tight to the body you could add a little mirror spoiler off the bottom edge, say maybe 10 inches ? i think.
22 inches sounds like a mighty long angle for something so short in stature. I like the after market mirrors shaped like a bullet, although the bullet is not a optimum shape, i will suggest that it is better then what is currently being widely employed.
Here's a photo of a 65 mustangs bullet mirror and a 69 Porsche's bullet mirror.