Dedup on 7z files not happening

Hi Everyone,

I have a 2012 server that i want to use to store month back-ups. I recieve them in the form of 7z files with max compression divided in 5GB file.
folder 2013-01
jan.7z.001
jan.7z.002
jan.7z.003
jan.7z.004
jan.7z.005

folder 2013-02
feb.7z.001
...

I installed a 2012 server en enabled dedup.
Copied 2 month to it and run the dedub command.
Result is savingsrate 1%.

Copied one of the folder to the same disk to test it and got 30% savaingsrate.

I was roughly guessing for around 40-50% here as most of the data is the same (on a other location I do the same on files and it works like a charm). So something is of here. For some reason MS cannot do it's thing.

Hopefully some can point me in the right direction.