Why Linux df command and Windows right-mouse properties show 16 TB on Drobo FS?

We have 2 Drobo FS/DRDS2A. We have 2 Drobo FS, with 5 2TB disks One Drobo allows for 2 disk failures and the the other allows for 1 disk failure. Below is a screenshot of the Drobo admin GUI. So 5.38 TB is the max available space. However the df command AND even the right-mouse Properties option in Windows shows 14TB or 16 TB of usable disk space. I’ve been Googling and can’t find anything about why this would be the case. Perhaps there is something with the CIFS or SMB version 1 protocol that is causing this?

What’s also a shame is these can only run the very insecure SMB v1, and there was never a firmware update created to mitigate this vulnerability.

From our Fedora Linux server I ran df -h|grep drobo
16T 848G 16T 6% /mnt/tmp