DD with BackupExec - deduplication and policies

hi all, need some help.

BackupExec server connect to DD via OST storage.

When create multiple policies (e.g testing), backing up the same oracle client to same destination (same storage unit in DD), how to explain in the DD file system, the datasets are not deduplicate as it grows until the backup set is deleted, and DD clear maintenance?

I wonder, if is it with different policies, BE will create different datasets (file format), and this datasets is not global dedupe.