The upgrading process is consistent - it's just an automated computer program.

Think of the upgrading process as a car engine. V inventory is the "gasoline" of the upgrading process (for lack of a better metaphor. I invite someone to please think of a better one).

Recently, the releasing of V inventory has been incredibly inconsistent. Without that V inventory "gasoline," the upgrading "engine" doesn't work the way you want it to.

Before FC was monetized, V inventory was much more plentiful on many of the main routes. Now, a lot of it is being held back until the last minute. That's why the upgrade that used to happen at T-6 or T-5 may now be occurring at T-2, T-1, or even at the gate.,