The chart on Ex Astris Scientia looks good but could it be wrong? The windows on the Ambassador quite a bit bigger than on the Sovereign, and even the vertical distance between the windows on the Ambassador makes the decks look spaced farther apart, when each deck should be about the same height. Almost like the Ambassador pic is blown up and the details aren't to scale of the other ships' details.
If this is true the Sovereign should have more volume.