beer -
As others have said, the Flow illustrator program we have used in the past isn't perfect, but I think it's good to use for this thread :
I like the louvers as a compromise because you can preserve rear visibility. "Eco-Louvers" would be different from the muscle-car louvers because they would NOT follow the slope of the rear window :
Instead the last louver would end up resembling a "CRX-style" flat window shape :
CarloSW2