We must remember that the FASA stats were all complete and utter bollax when you compared them to the actual ships, for example the Baker class which uses a connie saucer and nacelles and has a huge slab rear hull which is far bigger than the connie somehow masses several hundred tons less than the connie. FASA scaling is notoriously horrid. Their designs were also very unoriginal when it came to Federation and Klingon ships often just scaling up or down basic components from the Connie and K'T'inga respectively and slaping on a few wierd geometric shapes. I'd scale the D-16 by taking the command hull as being the same as that on the K'T'inga and working from there.