When I was a backup admin, one of my customers told me to keep a single tape for each day in the same volume pool. The best way for this is to create the volume pool scratch and use it as well, so don't use a fix rotation.
Why I'm telling you this? coz if you need a particular tape for each day you'll have to freeze another ones, expirate some other and it's kind disturbing to do that while you have the chance to use scratch.
It doesn't matter which tape is gonna be used for X backup, the only tape yoyu just need to keep in mind is the catalog one in case of a DR. The catalog handle the way the images are gonna be writen in which tape, date and etc.
Below I will give you a technote related to scratch.
http://www.symantec.com/business/support/index?page=content&id=TECH17904&key=15142&actp=LIST
How netbackup allocates media
New Backup which is first time allocation order:
1. A tape in dirve that has images on it is looked for
2. A tape in drive that has no images on it is looked for
3. A tape that has images on it is looked for
4. A scratch tape is looked for
When a tape reaches EOM, a span request is serviced by MDS.
The logic for span tape allocation order:
1. Look for a tape in drive that has no images on it.
2. Select a drive.
2. Look for scratch tape for a drive selected
3. Look for tape in drive that has images on it.
4. Look for tape (not in drive) that has images on it.
The scratch pool is an optional volume pool that can be configured within VERITAS NetBackup. If the scratch pool is configured, Media Manager moves volumes from that pool to other pools that do not have volumes available.