I don't think there is any right or wrong answer. It is personal preference.
Some people use them for blind spots, others to spot the back wheels.
I have mine set to spot the back wheels (and some of the blind spot) to make navigating in tight spaces easier, I have a 3rd smaller stick on mirror for the blind spot (I stuck it on the mirror arm so as to not obstruct the other mirrors).
They are such a PITA to adjust yourself, I never went and found the optimal angle, just one that is close enough to work for me.
Some people use them for blind spots, others to spot the back wheels.
I have mine set to spot the back wheels (and some of the blind spot) to make navigating in tight spaces easier, I have a 3rd smaller stick on mirror for the blind spot (I stuck it on the mirror arm so as to not obstruct the other mirrors).
They are such a PITA to adjust yourself, I never went and found the optimal angle, just one that is close enough to work for me.
