There are no "shoulds" in Hilton Upgrades. You could be the only person in the hotel and they may not upgrade you, other times they will be full and bang around on the keyboard for 20 minutes and give you a suite.

Don't ever plan on an upgrade. Enjoy it when it does happen, but if you want a better room, book it, don't count on the price or occupancy giving you any indication of the ability to upgrade.