SBS 2011 Standard backup retention problem

I have a SBS 2011 Standard, not Essentials, and the backup retention for the Server Backup to an internal HD is only 5 days though there is more than half the drive space still available.  I was under the impression that WSB will retain backups until the drive fills and then start removing the oldest backups. 

I thought the 5 day retention was a policy in SBS 2011 Essentials, not Standard.  I see no way to configure the retention policy for SBS 2011 Standard.

5 days of backups isn't enough.  I need to configure it to retain backups until the drive is full.  Anyone know how to go about changing the retention policy for SBS 2011 Standard's Windows Server Backup?