As far as I remember, military vehicles are one of the few cargoes in the game that already do take up more than one unit - it might be about 5, actually. If we're working on that as a basis, then I'd love to see human cargo taking up two or three units; if they were 5, then military vehicles would again need to be increased.
I'd love to see an increase though, one way or another. 2-3 units per human cargo seems like a nice compromise that I'd be happy with - still not realistic, but a better state than now, and at the same time doesn't compromise too much space for RP commitment. When possible I quite like to fly with a "crew" abroad in the form of the commodity, but having a fair sized ship (and thus fair sized crew) becomes less tempting if they're taking up 100-200 cargo space.