So to be clear: I don't like Spaces, but I can make them work: A Space a unit that corresponds to the configurable half of a quarter of a dton. So from the outside, a quarter-dton cube (1.5 meters on a side at 13.5m^3 for a dton - not so much at 14m^3, but let's try to imagine this like a deck plan for now. Humour me.)
If a deck plan was 3D, then a 'dton' would be two squares across and two high, and one of those squares would be the outside of a one Space vehicle. If that vehicle was a box (Structure with no power plant or locomotion) you could cram 2 Spaces worth of stuff in that box. If it's anything other than an empty box, it's less - again half full (half empty?) is the default, but if it's part of an airship, you only get a small little fraction to work with.
As long as I remember that and fill in within the lines, it all seems to work out without having to compute actual volumes of spheres, cylinders, streamlined shapes, or what-have-you (it also gives artists some freedom to... hopefully not make human vehicles look like monkeys... but that a different Chirper ball). It does mean that a 100 Space Structure with nothing in it (it's a box! or a shipping container.) can have up to 200 Spaces of stuff inside, but I've carefully fixed the internal bays (and added Docking Space as an option) so you can't start a Tardis chain of bays (as written, with the current VH you can do that... easily!).
So you've got that table I posted above. 10 Types of 'vehicles', 28 Features, and then you can still mess with your Spaces to add different (or multiple) power sources, change the range and speed further and then add options to the hull or interior to your heart's content. And weapons. If you want one TL6 jet fighter to have different characteristics than another, then you can make one Fast, the other Agile, throw on some more Range (eat Spaces for auxiliary tanks or whatever) and mess with the size of the machineguns or cannons. A hundred variations of a TL6 20 Space fighter (not to be confused with a spacefighter).