As for cargo bays, yes 4 million population is about the max per transport in Proportions, given highest tech ship sizes and components. I'd say it's generous too, realistically speaking. If this were SE3 and I could differentiate between cargo storage types, I might make it worse in terms of cost, because once you have four million people in a space ship, you have to keep them alive for months or even years in deep space... good luck doing that efficiently! Oh, you'll "just" have four MILLION cryogenic hybernation compartments? Ok... total price tag...
As for whether a cargo bay should be able to store more than its size, I think SE4 is too abstract and undetailed in its measurements to take all of the measurements literally. Also, bstripp is quite right that mass and volume are different things, and I would add that items like people or space fighters themselves are one thing, while the mass and volume of what is needed to keep them functional is something else. Unfortunately, they're all on the same scale (kT). In short, don't take the masses TOO literally in terms of imagining what they represent - they are only accurate as effective measures of what you'll be able to cram in a location, or not.
I would also say that I don't think a space fighter would ever actually have a mass of even ONE kiloton, unless it was something unlike what I and most SF writers have generally imagined, or was made out of hyperdense alloy or whatever (which would tend to make it vastly less maneuverable than a lighter fighter). SE4 though only has one measure of size, and a fighter also needs supplies, maintenance crews, launch space and so on. Also, in order to be able to design the components on a fighter and have a limit, integral sizes means they have to be more than one kT, since that's SE4's smallest measure. So, either you accept that that there is a lot of abstraction going on, or you imagine enormous fighters, or you decide that each fighter represents a squadron, or whatever. Personally, I tend to imagine each fighter as one fighter that is probably well under 1 kT, but for purposes of effective cargo space required to store a fighter and the personnel/droids/supplies/spare parts/ operating space & base equipment needed to actually operate it for months on end, that's what the size represents when in cargo mode.
PvK
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