Thank you guys, fir correcting me. I thought I had researched it properly, but I clearly didn't!
I saw one post that claimed it did not have a gain in the fuel economy by lowering the top, because the frontal area did not change. I disagree with that. Based on my knowledge of aerodynamics, the more streamlined, teardrop shape should provide some benefit because it minimizes the stagnation area that forms at the rear of any shape moving trough the air which adds turbulence and drag. The frontal shape is not a "flat plate" either, which should reduce drag too.