Firstly, I'd stay away from Append for Disk based backups. The reason is that all media (BKF files) in an "append family" share a common OPP, which is reset each time one is closed
Make all your jobs Overwrite only. Also from Options\Media Management, make sure that the option to "Use overwriteable media in the target media set before scratch media" is selected, or BackupExec will fill the disk volume before overwriting any BKF files, regardless of the OPP settings
set up media sets for
Daily
Weekly
Monthly
if you want to keep your dailies for one week only, set the OPP to 6 days, if for two weeks, set it to 13 days, etc
do the same thing with the Weekly and Monthly media sets