It looks like manufactured goods can go quite a few parsecs before they become unprofitable; but raw resources and agricultural products seem to stack up differently. A metric ton of dry white rice sells for ~US $400 -- and approximately 10 metric tons fit in a dTon. I am using
https://www.indexmundi.com/commodities as a reference.
Given this, it seems like an agricultural world will support only the planets within about five or six parsecs, while an industrialized world will trade much further. Perhaps manufactured goods don't trade at the full distance implied in the original calculations because a nearer world can out-compete on price with shorter transport requirements.
Even with the lower prices per dTon of raw materials and agricultural products, it still seems like they trade over a wider area than the OTU seems to imply. In well developed subsectors, the cuisine (including imported food) should change pretty gradually between maybe four or five regions, centered on the main agricultural producers.