"I was using it without the port shades and the lens hood, because I had a zoom gear on it"
It hadn't occurred to me to put the lens hood on the lens within the domes, so I tried that out today at home. On the Nauticam system, the lens hood will not pass through the N120 housing throat so has to be mounted from the front after the camera has been installed and before mounting the dome. That works fine with adequate clearance for the Nauticam 210mm dome and 20mm port extension. However there is insufficient radial clearance for use with the Zen DP-100 dome and the recommended 30mm port extension. There will probably be adequate clearance using larger Zen domes. The Nauticam zoom gear does not prevent mounting of the lens hood. It would be interesting to find out if using a lens hood within larger domes avoids the flare that is apparently sometimes an issue using full frame without external dome shades.