I concur with the 6-4-2 day window thing. Most of the time it happens this way. My upgrade had cleared by 3 pm PST yesterday on both segments for a flights on Saturday (6 days ahead of time as plat).

There may be some give on fare class. For a while as gold, I was clearing at the silver window, even though my ticket was clearly registered at gold.

They do seem to change algorithms periodically - although this may reflect my changing travel patterns more than anything.

OLCI at 23:59 before flight time is key for snagging upgrades at the gate. I have slid into many more than one upgrade by using this information. Often I was the only one to snag an upgrade at the gate.

Also, there have been several threads that state you need to be willing to give up the elite pre-boarding sometimes to snag the upgrade. I have done this as well.

This may be old advice as my upgrades have pretty much all gone through ahead of time since reaching platinum.

Good luck!