I've had a Chuck Harris eyeglasses mounted rear view mirror for 30+ years. I feel uncomfortable on the bike, when I have to ride without it because of rain.

If the mirror is mounted correctly, you must cock your head slightly to the left to see behind you. Chuck would stand behind you and see how they worked. He'd then bend them to make a final adjustment. Like all reflections, direction is reversed. If you find yourself turning too far leftword for comfort, then you have to bend the mirror to the right. Ditto for up and down.