[abwmma]

Let me try my best to explain how I did mine. I learned it at the BMW Club meeting.
Get in your driver seat with the normal driving position. Driver side window closed.
For the driver’s side mirror: Lean your head until it touched the driver’s side window. Adjust the driver’s side mirror towards left until the outside of your car no longer shows.
For the passenger’s side mirror: Lean your body so that your head is in the middle of your car ( or center of the rear view mirror). Adjust the passenger’s side mirror towards right until the outside of your car no longer shows.
I owned a E36///M3 (comes with a very small mirrors). It works for me. But for X1, I experinced it is a little too much. I used the B pillars instead of the body of the car.