Your current parameters looks ok. Here is some info from TSM:
"The db2adutl utility is used to manage the DB2 objects that are saved to
the TSM Server. When the db2adult is used to delete a database backup
object, the command that is issued to the TSM Server attempts to mark
the object for immediate expiration. For this deletion to occur, the
Backdel parameter must be set to YES for the TSM node. After setting the
object to be marked for immediate expiration, it will no longer be
accessible and will be directly removed during the next Expire Inventory
on the TSM Server. If the Backdel parameter is set to NO, the deletion
command will fail and the DB2 processing will transparently make a
second deletion call for the object to be marked as inactive on the TSM
Server. Then, based on the retention parameters for the MgmtClass, which
are often recommended as VerExists=1, RetExtra=0, VerDeleted=0 and
RetOnly=0, these parameters would still cause the DB2 database backup
object to be removed during the next expiration processing. "
You can use select * from backups... to look at the backup objects from the TSM client, but I don't think there is a funtion within TSM to delete individual backups. I may be wrong... I think it's better to post your question on the TSM forum (if there is one) or opening a pmr with TSM.