Basically, through geometry, you should be able to simplify the multiple fins into one larger fin by finding the angle where you have a total eclipse of the window in reality. Then work backwards to find a single fin that eclipses it at the same angle.
Have you checked out this blog?
http://energy-models.com/blog/11-11-10/simplifying-shading-equest-and-trace-700
Basically, through geometry, you should be able to simplify the multiple fins into one larger fin by finding the angle where you have a total eclipse of the window in reality. Then work backwards to find a single fin that eclipses it at the same angle.