Portsmouth, as far as I can see, is only modelled to give a bit of scenery for Solent voyages past the IOW and no doubt to show off the excellent Spinnaker Tower.
There was a discussion about whether we want Portsmouth in the future, but there are so many suggestions for other ports, that who knows.
Personally, that is my favourite commercial port and I would love to see it modelled. (I go there often enough). but as the interior (North) of the port wasn't modelled they haven't needed to accurately model the sea bed.
Stu