First, my 3 rows building slots is not the same as sudkks. Well, it is from his version 1.0 and likely never needs to be updated unlike his more complex current version. Also, sudkks can make you what you want for four rows in about 20 minutes whereas I must learn first before I can. Not a problem if I come up with time.

Next...
https://images.steamusercontent.com/ugc/17119402287080772733/B2B1B22E66081358AFCAA11D30147BC41E24935F/?imw=5000&imh=5000&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

I have 396 mods loaded in this screenshot totally reworking basically the entire game to be a super slug fest.

This screen is loading only the +8. If I add the +12 submod, it is the same. The primary settlement is much smaller than the 18/12 no matter faction.

If I may suggest, base upon the BSE mods for your Primary settlement slots and then only make the 8 and 12 minor settlements mods based on the BSE +6 and that gives you back MIXER compatibility as well.