The Skill and The Wit (spoilers all RotE books)

['thul]

The culture of the six duchies was a closer "fit" to that of the elderlings than say, that of Chalced. It has been made abundantly clear in the books that Chalcedan morals and opinions have imprinted heavily on Jamaillian culture. Thus it could stand to reason that the "harlot queens" as the elderling queens were named in Homecoming stems not from Jamaillia, but from Chalced. Especially when considering that the rulers of Chalced were traditionally opponents of dragonkind/elderlings.

One thing you might have forgotten to consider when defining "the center" of elderling rule is that the era of the elderlings was not something that went in a matter of years or decades, but in a matter of many centuries or millennia. Even with extended lives the society will fluctuate over thousands of years. What may be the capital at one time might be a small backwater a few hundred years later. The island Icefyre chose as his resting place was once a major Elderling hold. As was Kelsingra. Same for Fregong. And buckkeep (or whatever they named that place so long ago).
Dragons did not care much about borders, but humans and Elderlings did. Thus their realm would change size and shape over time. Obviously Elderlings would fight those that would use dragon parts in medicine. Sometimes they would win, other times they would loose. Chalced is obviously a place where dragon-foes won out more than they lost.