I think we're talking about the Upgrade Standby list inside of three hours, which is discussed here:

Priority within 24 hours
New waitlist requests for MileagePlus Upgrade Awards, Regional Premier Upgrades and Global Premier Upgrades can be made until 24 hours prior to departure. If we haven’t confirmed your upgrade by the time you check in for your flight, you will be added to the Upgrades list at check-in, so there’s nothing that you need to do after submitting your original request. Our upgrade systems process requests, per the priority listed above, until three hours before flight departure, at which point our gate agents will handle all remaining upgrade requests. Learn more about the upgrade standby list.

The "Learn more about the upgrade standby list." link is the text that I posted above, which seems (to me at least) to indicate that Elite Status is the first cut, not fare bucket.