[f5fstop]

If I could have installed my rectangular fish eye lenses on the outside, I would have put them on the outside top of the mirror. The outside bottom is still a location where you can actually see a vehicle. By installing the mirror in the outside bottom, you block this area for seeing a vehicle two lanes over. Outside top basically shows nothing in way of active vehicles.
However, due to the large red leds in the signal mirror, I placed my fish eyes on the inside top.
I do believe a person tends to look at the outer edge more than the inner edge, so the outside area is probably better.
I do adjust the mirrors the way stated in the above article. It makes more sense, and helps to avoid running over cars.

However, the best place to install is where YOU, the driver are confortable with, and will use when changing lanes.