1) Under Tools --> Options ---> Media Management, you should set the Media Overwrite Option to Overwrite recyclable media contained in targeted media set before overwriting scratch media. BE will then re-use the recycleable .bkf files before creating new ones.
2) For the B2D folder properties, increase the Maximum number of backup sets per backup to disk file. This will allow BE to put more backup sets into each files before creating new ones.
Lastly, although you can set your job property to Append, this is not advisable as the OPP starts from the end of the latest backup job.