D5-300C Can't have 2 disks in bay 1 and 2 at Single mode

[nox]

I cannot have 2 disks in the first 2 bays when the DAS is set to SINGLE mode. One disks wont be detected correctly:
In my setup I have a 16TB (TOSHIBA) and a 1TB (SAMSUNG) disk (which are formatted with BTRFS, the 1TB extends the 16TB file system). So naturally I want to have these disks together in the first 2 bays.

But having the HDDs there results in one disk not being detected correctly (detected as only having 0,5 KB of space):

Screenshot_20230616_182218.png (9.98 KiB) Viewed 1300 times

Screenshot_20230611_131815.png (10.18 KiB) Viewed 1300 times

The Raid modes seem to work correctly, but are not applicable for my situation and hardware:
RAID 0 results in a logical 2TB disk and RAID 1 in a 1TB.

Also for some reason there is an undocumented mode which I'm not sure about:
If I turn the dial to the down position - which isn't labelled - it results in combining both disks to a logical 17TB one. Maybe you can provide more information about this mode and how reliable it is.

[nox]

I'm on Linux,

this is how Disks (gnome-disk-utility) shows the drives:
When the 16TB drive is in bay 1 or 2, and the 1TB drive in bay 3:

When both drives are in bay 1 and 2: