Default N9005 nandroid backup - CWM - Backup Size?

I've just made a nandroid backup from cwm recovery to my external sd card. I have the 32gb variant and the 16gb is used but my nandroid backup made by cwm is 3.8gb.. I've searched in the cwm menu for more options to backup my phone but i didnt see any. e.g. full backup etc. It only has backup and advanced restore? I think that the size of the backup would be 16gb.. Have I done something wrong?

Sent from my SM-N9005 using XDA Free mobile app