Die PF auf de EX 2013 werden nicht durch den fehlenden SIS sondern auch durch.
https://social.technet.microsoft.com/Forums/ie/en-US/b5ef9556-a94f-40cc-ada0-651cac593b6b/mailbox-database-on-disk-size-increased-hugely-during-mailbox-migration?forum=exchangesvrgeneral
"When moving a mailbox from a previous version of Exchange to Exchange 2013, the mailbox size reported may increase 30 percent to 40 percent. Disk space used by the mailbox database has not increased, only the attribution of space used by each mailbox has increased. The increase in mailbox size is due to the inclusion of all item properties into quota calculations, providing a more accurate computation of space consumed by items within their mailbox. This increase may cause some users to exceed their mailbox size quotas when their mailbox is moved to Exchange 2013."
Das erklärt das Problem nicht für den EX 2007, ihr solltet das aber mit im Blick haben.