The side-mounted rear-view mirrors on our new FJ Cruiser are roughly rectangular in shape, mounted with the long side vertical (usually the long side of these mirrors is horizontal). Debbie and I both immediately noticed the poor vision to the rear, especially when compared with our Tundra trucks.
With a little analysis, it's easy to see why. I won't bore you with the trigonometry, but...with the driver sitting 30" from the 5.5" wide left mirror, the field of vision is only about 10° wide. On our Tundras, with their 8.75" wide mirrors, it's about 17° wide – definitely a noticeable difference!

A driver's-perspective view of the left mirror shows how much this improves the field of vision. My rough estimate is that I now have a 40° field of view, a vast improvement over 10°
If we drive with these for a while and still don't like them, I may commit FJ sacrilege: install big-rig style tripod mirrors on both sides. Those mirrors are hell on the drag coefficient, and would probably drop our highway mileage significantly, so I'm hoping I don't have to resort to that. One other possibility occurred to me: cameras installed on the mirror mount (perhaps on the bottom of them), displaying on screens over my head. That might work as well.
Why did the FJ designers make such a wacky choice for the mirrors? The only reason I can think of is that some designer thought the vertical mounting looked better, and didn't care what that choice did to the driver's visibility. We curse this designer daily...