There is no ‘one way’ to set mirrors. What you want to know is where your mirrors are aiming for you. Personally, I like to see just a sliver of the side of my automobile in my side mirrors.
The key is to not have to move your head or adjust your body in order to see in any of your mirrors. …To be able to see in each by just moving your eyes so that even when you aren’t consciously looking, your subconscious is still taking in what is going on behind you and next to you. And when consciously looking, you can update and validate information with a glance.
