Capella is just a useful model for 'the total population of Terran colonies'. You bring up a good point when talking about the distribution of that population, but it's almost irrelevant: Delta Serpentis would need to hold on the order of 1 billion people if it were the focal point of Terran emigration from Sol, and it's right near the front lines of the Terran-Vasudan war, two jumps from Antares and some of the heaviest fighting of the war. Even if it's the safest place in Terran space it's not very safe...and meanwhile, Antares, Adhara, Regulus, and Luyten 726-8 need to gather enough population and infrastructure to become the central powers of Terran politics during the Reconstruction period. Antares is a killing ground, and Regulus is an actively Vasudan system. There's basically no question that millions of civilians were at or near the front during the 14 Year War.