It is easier to put your head against the window and move the mirror so that you just see the edge of the car and put your head over the center console and do the same for the other side. It absolutely boggles my mind that 95% or more people set their side mirrors wrong. How do I know? I can see all your damn faces in the side mirrors when I'm behind you. You should always still check your blind spot when you change lanes. Extra safety is good, some cars still have a bit of a blind spot, and a car can easily move from your rear to your side mirror in the time it takes to check them.