Current setup doesn't tie what you want together it seems.. so go SQL.
I am not sure if this is solid, maybe someone else can further adjust or verify; but SQL Alert with a Group Member Trigger?
-----------------------------------------------------------
WHERE
(
(Containers_AlertsAndReportsData.GroupName = 'X')
)
SELECT Volumes.VolumeID AS GroupMemberVolumeID, Volumes.FullName AS DriveName
FROM Name
WHERE
(
(100-NullIf(VolumePercentUsed,-2) <= 5)
)
-----------------------------------------------------------
Since you can't change the headers, there is adjustment.. again this I am sure would need some work.