Ah, I hadn't looked at the other replies when I posted my 'puter query.
On the CoG issue, I think DJI assumes that the FC will be mounted at (or over) the CoG point. In this case, the CoG is also the "Central Axis of Movment", the point around which the MR pitches, yaws and rolls. With the DJI Flamewheel setup, for example, the FC goes between the top and bottom frame pieces, in the center, which gets it close the that "central point". But other applications use the Naza in another airframe. In my case, it is being used in either a Gaui 330sx or a Gaui 500x-- as suggested by the Gaui assembly instructions, the FC is on the top board and offset from the center, with the radio Receiver being placed on the other side of the offset. I can see, from the FC's standpoint, that the gyroscopes and accelerometers should be placed near that axis of movement since that affects how they react to the pitch, yaw and roll motions of the aircraft. This may be cutting things too finely, I suspect that it could be off by a small distance (an inch or so) with no consequence. Or so my suspicion assumes.
But the GPS puck, OTOH, is another issue-- since it is customarily mounted several inches above and to the side and rear of the"CoG" point, the x, y and z coords of that mounting location need to be input for the config.
Enough of this late-nite esotericia...
--Bill