I'm not sure I understand the issue. Bitlocker is capable of encrypting the OS volume and 'fixed data volumes' (as well as removable storage via Bitlocker-to-go). Are you saying that manage-bde -status does not show these partitions as valid volumes to be encrypted? Or, are they showing as 'data volumes' in the manage-bde -status output and not being encrypted via your MNE policy?
Yes. Bitlocker does not show these partitions as valid volumes to be encrypted. I don't know why. But this issue occurs only when McAfee MNE is installed. When I uninstall MNE and try encrypt disk manually, Bitlocker recognizes all disks and partitions properly.