Yeah, I think the days of the week matter for this flight... I have talked to folks who used travel packages that include F for a modest bump, so when people are cruising or headed to a vacation on the beach they just throw in the extra little bit of cash to make it a "special" vacation. But if you fly say on a Saturday when people aren't doing that, the upgrade chances are good. If it's Thursday, everyone's headed to their long weekend and you are hosed.