I agree a guy should check to se at what power the reticle is calibrated at and yes it is a little different with all three 6-24s I have. Trying to figure out what power they where calibrated at is what led me to find the MOA thing.What I do is turn the power all the way up and dial it down till the hashes line up with the inch marks on the yardstick. I actualy set it so that 10.5" is the distance it takes 10 hash marks to cover and 21" for 20 hashes to get as close to MOA as posible? I found it is more acurate to turn all the way up and dial down to the new MOA calibration marks I put on the power adjuster.
I dont pay any more atention to the power # than I do the range # on the side knob,near as I can tell they where just guessing and not very good at it! What matters is the power dial is turn to the calibration lines I put on it!
18x + or - has ben working very well for shooting prairie dogs as mirage is ususaly too bad to use much more power than that anyway.
I can see why someone who knows Mills would like them and I have to use them in the fixed 16Xs but MOA just works so much easier for me.
As for helping with the reasoning I cant help...Note my signiture line,heck I'm just a reTIRED dairy farmer that welds mineing boxes for a liveing.
If it works I run with,if it doesnt I mess with it till its FUBAR