Is this correct?
Will i then have a weekly backup including only all NEW full backups created during that week?
The problem is that once the specified retention is reached, backup copy job starts transforming on daily basis. So to say, the oldest restore point (full backup, .vbk) will be moved forward once a day. From perspective of files to tape job, it will be completely new full backup that has to be copied to tape mediums.
So, weekly mediaset will contain about 7 full backups, plus, 7 increments that must be transformed in order to set reference to newly-moved full backups, plus, weekly GFS points. Not sure whether it is something you're after.