With hardware compression, Backup Exec does not determine or configure the compression ratio. Backup Exec just sends the data to the hardware for compression and the hardware tells Backup Exec how much the data was compressed.
First I would check to make sure that the drive you are backing up is not compressed. tape drives can't compress data that is already compressed.
Second I would verify that compression is getting enabled in the backup, use the following technote for that. http://support.veritas.com/docs/287662
Hope this help a bit.