As a relative noob to AS MVP, coming from over a decade of experience as an elite with CO/UA, I'm caught in the same confusion you are.
Sometimes, I'll get upgraded on time.
Sometimes, I'll get upgraded a full 24 hours BEFORE my MVP window opens. ?!?
Sometimes, I won't get upgraded at all, in spite of zero F seats assigned at check in.
Sometimes, I won't get auto upgraded, but I'll keep incessantly re-checking-in, and several hours later will be able to "BUY" an upgrade, which then prices at $0 due to my status. ?!?!?
Frankly, to me, AS's upgrade system is a big ol' ...?!?!?!
But, in spite of that, I still get a LOT more upgrades on AS than I was on UA for the past three years.
I've even been upgraded on the ANC-SEA run, as a lowly MVP!
And I'm fully aware that a seat map isn't an indication of F booking levels. Except it often is, because MOST people who buy tickets also choose seats. It was a good indicator at UniCont, anyway. It was at least something to start from.