Makes me wonder what the OTU would have been like had it followed that path . . .
I prefer the small ship universe feel but the logic of the world stats dictate that it has to be a big ship universe which has always been a problem for me. My solution is it doesn't all have to be a big ship universe.
If you think about the world stats then the systems with high pop and high TL are going to be many orders of magnitude more wealthy and powerful than the rest so the alpha systems are the only ones the Imperium needs to care about and so I think it's quite plausible that they are the only systems the Imperium does care about or more fully:
1) alpha systems
2) systems that are possibly on the way to becoming alpha systems
3) systems that are physically close to the alpha systems
4) systems along the main communication routes between alpha systems
5) systems being built up for some reason e.g. as a border fort.
If you mess around on travellermap.com then you find there's usually only 1-3 alpha systems in a sub-sector (often just one) and maybe 4-6 of the second category which often overlap with the 3-4 in the third category plus a few in the fourth and fifth categories.
So all you have to do to create a half-big, half-small universe is say the Imperium simply doesn't care about the small half - or rather it cares enough to fund detached duty scouts as an early warning system but that's about it.
That change means you can have about half of space - in any sub-sector, even deep within Imperium space - as your SSU.
edit:
random example Dagudashaag sector / Remnants sub-sector near the center of the Imperium, roughly five sub-sectors spinward of the capital
http://travellermap.com/?scale=22.625&x=5.614&y=17.049
has only one alpha system (my working definition being pop 8+ and TL 12+) and as it doesn't have a class A star port which is my strict definition of alpha system I wouldn't have that as an alpha system either. (I'll need to dream up a list of reasons why systems like that which ought to be a big deal don't have high enough star port e.g. they're xenophobic and made a deal with the Imperium to be ignored in exchange for not building star ships or they're rebellious worlds that aren't allowed to build star ships.)
However there are six or so alpha systems just outside the sub-sector so a plausible setup might be that because the hinterland clusters of those surrounding alpha systems overflow into the sub-sector those outside alpha systems tend to dominate it making the edges of the sub-sector part of the BSU but most of the central part SSU.