That's one way to incur administrative costs I spoke of earlier.
It should be like, some quadratic function with argument x=(a+b)-2, a = number of bases, b = number of personnel (in some multiples, like 20?); this function could impart additional maintenance costs. So you can have 1 base with 20 personnel w/o any extra costs, but the costs start to rise after that. With 16 bases and 600 people, you'd have x=44. If, say, increase was 1.05^x (cumulative 5% per level), your maintenance would be, in this case, about 8.5x nominal. Okay maybe that's a bit too steep but you can see where this game is going
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This is quite fun formula as you can keep strong force of soldiers and many bases, yet don't suffer much, since most of the manpower are always the workers. Eg.: 50 soldiers + 30 scientists + 80 workers = 150, with 16 bases that makes x=21, and the maint. cost increase 2.8x nominal.