Hey RR, I have tried the mirror trick too. What I notice is the "middle" adjustment is sometimes not the same as lining up the crosshairs in a mirror. Close.

In other words, if I center the scope by pushing to the extremes and setting in the middle, sometimes the crosshairs do not line up in the mirror.

Never knew which idea was better. I guess the end outcome is to get maximum adjustment along with trustworthy MOA adjustments, which you won't at the edges.