I really don't know why people struggle with the MIN/MAX concept so much. It's pretty simple. When a base has MIN below the current number of pilots, any attrition for that BES won't be backfilled until reaching the MIN. So if you have a BES with 500 pilots currently, a MIN of 490, and a MAX of 500, Crew Planning would allow the base to shrink by up to 10 pilots. They aren't requiring it, but would permit it. Now why they do this could be two different things. 1) They're doing it out of training considerations, which is what most of the current vacancy bid is. These are growing fleets and it doesn't benefit the company to reduce the number of CA long term, but due to training throughput they need to limit potential activations into those categories which would trigger a training event. 2) The base is intentionally shrinking. You're starting to see some of this on the 756 fleets in particular, as well as IAH 737. It's obviously not in danger of closing, but prior to UPA23 they grew it far larger than their optimizer said it should be because it's where they could get pilots to upgrade. So they've been right-sizing it over a period of time. At one point it was up to just over 800 FOs, but has been reduced down to the current 646 through attrition.

The net result is that reducing the MIN for any BES limits the total amount of movement on this vacancy. All of these widebody CAs will be coming from WBFO and NBCA, almost exclusively. A WBFO taking a WBCA will create a new vacancy that must be filled because the MIN is set to force a backfill. A NBCA doing the same thing likely won't in most domiciles.

We've all heard that a single WBCA vacancy can create [insert number somewhere between 5-12] vacancies due to the cascading backfills. That presumes, however, that each of those positions must be backfilled. Hypothetically, if that number was 8 vacancies created per WBCA vacancy and there are 92 WBCA vacancies, there could've been 736 people moving on this vacancy purely as a result of the WBCA vacancies. That won't be anywhere close to the case because of how they've done the MIN/MAX.