calculation for free space after VTL deletion

Hi there ...

Can anybody tell me how to calculate free space after VTL deletion?

Example ...

# vtl tape show all

Barcode    Pool      Location               State      Size             Used (%)    Comp   ModTime           

--------   -------   --------------------   -----   -------   ------------------   -----   -------------------

DD0001L1   Default   SCP_Admin slot 21      RW      300 GiB   298.0 GiB (99.33%)      1x   2017/04/11 16:00:18

DD0002L1   Default   SCP_Admin slot 21      RW      300 GiB   298.0 GiB (99.33%)      1x   2017/04/11 16:00:18

Delete aboveVTLs should make 596GiB ( may be bit less as Metadata need to be considered for 0.5% as per https://community.emc.com/docs/DOC-31725) as Comp 1x . BUT in real life .... It only creates 446.8 GiB reduction of the space ... see below output after deleting VTLs.

Before Deletion ...

# df

Active Tier:

Resource           Size GiB   Used GiB   Avail GiB   Use%   Cleanable GiB

----------------   --------   --------   ---------   ----   -------------

/data: pre-comp           -   122833.0           -      -               -

/data: post-comp     7715.0     5864.3      1850.6    76%             0.0

/ddvar                 78.7        3.7        71.1     5%               -

----------------   --------   --------   ---------   ----   -------------

After Deletion of VTL

# df

Active Tier:

Resource           Size GiB   Used GiB   Avail GiB   Use%   Cleanable GiB

----------------   --------   --------   ---------   ----   -------------

/data: pre-comp           -   122831.5           -      -               -

/data: post-comp     7715.0     6311.2      1403.8    82%           455.5

/ddvar                 78.7        3.7        71.1     5%               -

----------------   --------   --------   ---------   ----   -------------

How come only 446.8 GiB is freed .

( if  Comp 1x is actually x 1.33 , it does make sense .. so would Comp 1x is round about in output display ? )

thanks

aya