Look at the Jenolan model, particularly the windows. It's way
more than a few decks thick. If those are Constitution class nacelles (and they are) and a Constitution-class bridge (and it is), the Jenolan is a pretty darn big ship. I don't know why everyone thinks it's so small.
Here's a 1/1000 scale Jenolan model next to a 1/1000 scale Conny model: