When I was getting my license 20 years ago, I don't remember the instructor going into specifics how the side mirrors should be adjusted - it's fine as long as you can see behind you.
Even during the driving test, all I had to do was pretend to adjust the mirrors and the examiner will give me a tick for that part of the test hahaha
My grandson just finished taking driver's education he'll be 16 in February and can get his license then. I will have to ask him if they covered adjusting the mirrors. I have no idea whether they did for me, that was far too many years ago!