Prius rear window more mysterious than the movie

I don't know if this is the right forum for this question but I will post it anyway.
I discovered yesterday when driving east in the late afternoon, the sun was blazing toward the back of the vehicle. What I was surprised to see was, when looking in the rearview mirror was, the bottom portion of the rear window had absolute clarity compared to the top pane of the window when looking at the car behind me.
Were the Toyota engineers cognizant of this effect when designing the car? The split window pane in the rear of the Prius is often discussed as a feature that takes adjustment for most new Prius owners. Everyone aware of this nice feature?