Backup Exec 2010 R2 Backup to Disk Settings

I presently have Backup to Disk configured with the following settings:

Maximum Backup to disk files set at 600GB
Allocate Maximum Size for backup-to-disk files disabled
Maximum number of backup sets per backup-to-disk file is 100
Low disk space threshold disabled
concurrent operations allowed: 1

The drive I am backing up to has 800GB usable space...

I have 2, B2D files one with total capacticty of 464GB, the other with 456GB - presently used is 455GB and 365GB.  I'm getting disk space alerts for these jobs, as when the B2D get full, the disk space gets low to a few hundred MB - but the jobs are completing.

I don't believe the B2D settings are set correctly, and would like them set to only use 800GB of disk space, so they dont drop my disk space size to only a few hundred MB and potentially fail future backups.

The size of my backups jobs is about 230GB for differentials, and 654GB for full backups.  Differentials are run Mon-Thurs and Fulls on Fri.

Can i Just change dthe maximum size for backup to disk files to 400GB each? Also how will it prevent from having a 3rd B2D file created? I recently acquired this environment, so not sure why there are 2 B2D files to begin with with such a high setting.

Thanks.