I just did a test with my grey card and the Gossen would underexpose by about half a stop using reflective vs incident, but that may just be my grey card!
Just a little update:
THE DOME FOR THE LUNA STAR F2 WILL FIT THE GOSSEN DIGIPRO F.
I ordered the dome from B&H and it came in the other day. Snapped onto my Digipro and everything seems to be working fine. Just thought I would update the thread in cas anyone in the future has the same problem :)