@zDarby - The smaller Constellation number is due to the way the primary hull is assembled and the way I cut the volume up. You can see in this screen cap
that the Constellation takes just the top of the Constitution primary hull and puts one on the top and one on the bottom of the thick body. The volume for those top pieces added together is 91,576m3. To get the rest of the equivalent primary hull volume you would then subtract it from the combined cargo+engineering volume. In that sense, the Constellation is pretty flexible in how much volume can be designated for people, shuttles, cargo and engineering. Here is a graphic of how it is sliced up.