"The reticle for the 1.5x6 is a little bit bigger and yes it would be calibrated at 6 power, the subtensions are the same"
So there you have it. I was correct in my speculation that the reticle was just sized differently so that both worked out to be the same subtensions at each model's respective maximum magnification.
Some of you may be shaking your head and thinking, "Duh!". Some of this stuff is new for me though and I know I have seen others on the web trying to figure it out as well. I hope this helps them if they are searching for answers.