It is not however more population than Epidauros, and is certainly less than both together. I would not risk endangering the accession of the two new league cities by ripping away the chance for them to colonize the easiest and nearest site, and as Linos says this is a terrible example to set for the league cities by saying that league rules don't apply for Eretria and her endeavors if they don't want it (although they'll be inflicted on you if you go against it and are weak, as with Ankon earlier). Plus, I would contend that even if those 700 were not almost made up through immigration within a mere 25 years, it would be more useful to have it take some citizen immigrants from the local cities. They actually know the local conditions and could serve as an invaluable trove of information to the refugees of Kymai, who have only known very different barbaroi and agriculture in ash-nourished volcanic lands. We want them to land on their feet and not stumble, but if we restrict citizenship to Kymai only then they cannot benefit from this local knowledge.
It was brought up before, but I disagree. The main driver in our immigration is the wage and opportunity available in Eretria, since that's the only city of ours that most have heard of. If we have massive emigration to the colonies from the choice land and opportunities available out there, then that spikes up wages in Eretria as the labor supply becomes less. The high wages drive general migration to our city, and once they arrive and become aware of a good number of the colonial opportunities a good fraction immediately set sail to the colonies. It's a feedback loop that continues as long as we have available land, with the immigration to Eretria being driven by the 'pull' factor of wages towards Eretria. This is most maximized by having desirable colonies hoovering up everyone who thinks they can make a better life from Eretria, that is, a 'push' factor towards the colonies in the form of choice available land. To maximize the pull in, we must maximize the push out; that can be done if we have many attractive spots available (that is, more sites available for colonization) to limit the rate at which any particular one's desirable land is parceled out and provide different circumstances amenable to the whims of the people. For instance, some may prefer island living and others living on a mainland.