Wow. That seems like an oversight to me. I'd hit up Support to make sure that's not a bug and then if it isn't at least put in a feature request for it to change.
So it looks like there's two percent availabilities, one for the group itself and one for the group members. If you just need the group itself then it should be fine to just use PercentAvailability, otherwise you may need to do something custom for PercentMembersAvailability for your report.
My first thought is using a case statement and the Orion.ContainerMembers table (I'm doing this all through SWQL) to custom count it, there might be easier ways, but this is what came to mind first:
avg(case when status = 1 then 1 when status = 9 then 1 end) as [newavg]
FROM Orion.ContainerMembers cm
group by cm.Container.Name