When searching for UA business saver flights, I normally see more I inventory available than O. Is this generally true?

If so, using the ANA tool, if I see a United business saver award available, is there a good chance that upgrades are available as well? I ask because I'm trying to upgrade a flight, but because there are no economy saver awards available, I cannot see any I inventory on UA.bomb. So just wondering if the availability of O seats is any indication of I inventory.