OK the problem you have got with using the same tape day after day until it is full is what happens to the job that is actively running when the tape fills up?
In the case of a library we will probably find another suitable tape, but with a stand alone tape drive all we can do is ask for a another tape (having ejected the initial tape as it is full.)
The next problem is say you start with an empty tape and write the first backup to it (let's say that backup started at 20:00, ran till 01:00 the next day and uses 15% of the tape). This backup repeats every day and uses approxiately the same space every day and is appending) After 6 days of backup 90% wil be used and the 7th backup will fill it it up, eject the first tape and ask for a different tape. The 2 week overwrite protection you have set for that tape will start at the time the tape fills up (in fact it will have started at 01:00 at the end of the first job but then moved back to 01:00 after the next job etc, until the point of time that it fills up. So now your tape with a 2 week overwrite protection can only be used about 3 weeks after it was first used, not 2. Hence Backup Exec keeps it's overwrite protection for longer than you expect
It is therefor probably a better strategy to not try to completely fill the tape but to stop using it on the last job that will fit in the remaining space. For the same 15% per day, 5 hours to run each night scenario. This would mean set your backup jobs to start as append, switch to overwrite if no appendable available and set the media set to Append period 6 days, overwrite protection period 13 days, overwrite recyclable before scratch (and makes sure whoever changes the tapes knows he /she needs to change them on a specific number of days)
Now against best practices you should probably think of this scenario
If I try to write 10 days of data onto 1 tape, what happens if have a disaster (after the 9th day's backup) where this failure takes out my server and damages the one tape cartridge I have been writing my data to. Basically best practice for tape backups is don't write a consecutive sequence of backups to the same tape. OK I know the usual response to this is along the lines of "tapes are expensive", but is a few more tapes in your environment more costly than the data loss you might experience.
As such I would say you need to rethink your strategy to use a few more tapes (at least have 2 tapes that you change daily so consective backups are on different tapes) and because you are using a stand alone drive, don't try to fill any one tape, instead stop using them just before they fill, keep them for 2 weeks and then overwrite them (and set appropriate append and overwrite periods to achieve this) and definitely DO NOT use the None setting for the protection of your tapes as if someone inserts the wrong tape (worse case even being a tape you need for a restore) and a backup jobs starts that tape will be overwritten
Finally the protection of disk based backup sets does not use media sets or overwrite protection periods, it is purely a time based control that uses your retention settings and the sets are deleted in the background once they expre. Please read up on Backup Exec Data Lifecycle Managemenet (DLM) for more info on this.