The 1200 wasn't intended to take multiple internal floppies. That's why the first drive on the external port is DF1:, whereas on the big-box Amigas it's DF2:.
Micronik made a dual-floppy cable for their 1200 tower kits that would remap DF1: to be an internal drive, but I think there was some circuitry involved. Not going to be easy to find these days.
