Prius and Kayak travel in harmony

I bought a Kayak recently and was happy to discover that not only is it possible to transport a kayak on the roof of a Prius, the car seems almost designed for it. The kayak is strapped down to the car with 2 small soft foam blocks protecting the car. The curve in the roof actually allows the boat to rest a lot lower on the car than it would on a normal car. The salesperson commented on this when he showed me how to put it on the roof.

I averaged about 46.2 mpg with the kayak on the roof as seen in the picture. With the kayak pushed back farther on the roof I actually did much better with 49.7 mpg but it seemed less safe as it angled the front of the kayak upwards. It can't go any farther forwards because then the rear foam block causes the roof to dent. These averages were gotten on the same 120 mile drive at roughly the same speeds. Though some unknown variable may have caused the difference in MPG perhaps? I usually get 50mpg.