You are in luck here, because there is actually a book about this: From the Indian Ocean to the Mediterranean which specifically focuses on the correspondence archive of a community of Armenian merchants based in Isfahan. It is theoretically grounded but I remember it being quite readable and full of great little details, if you are comfortable reading the sorts of books that would be assigned in a first or second year history class I would recommend it if the topic interests you.

Admittedly the timeframe here is post-Medieval, in fact for historical and source reasons it tracks the fortunes of Safavid Iran quite closely, but it does match with the body of your question. And in order to discuss the specific case of Armenians it is important to understand the general concept of the "trade diaspora". Before the modern world communication was slow and legal processes arduous, which introduces significant friction to commerce that is any more complex than simple cabotage (traveling port to port engaging in the ad hoc exchange of goods). Some of the earliest writing we have deals with this, like the complaint written in Ur around 1700 BCE of Nanni to the merchant Ea-nasir that the copper he obtained on a trading expedition was low quality. One of the ways of smoothing over this friction is through mutual communal bonds. If Ea-nasir was not just a seller to Nanni but instead, say, had married his cousin, then he would have a powerful incentive to deal fairly and well, and Nanni would be able to entrust larger and more complex orders to Ea-nasir confident that he would be dealt with fairly.

To give a concrete example of how this might work, a treasure trove of Assyrian documents from around the same time unearthed in the modern Turkish city of Kultepe, then Kanesh, shows this in action. Frequently trade was conducted among families that were split between Kanesh and the Assyrian capitol of Assur. So, say, a father might remain in Assur while his sons go to Kanesh. The personal bonds can overcome the friction of distance.

This same logic can then apply to social groupings that are larger than a single family if they form a tight knit community, for example minority groups that have a degree of social precarity and thus prefer to rely on other members of their community rather than the overarching political authority. A classic and very well studied example comes from the Jewish merchant community of Medieval Cairo, which fortunately had a tradition of preserving documents such that they have been well studied by modern historians. The social ties allowed for much longer distance and more complex commercial activity than would have been possible with formal legal means, both because these networks crossed political boundaries and because the threat of social censure was more immediate than the threat posed by the slow and highly corruptible Fatamid court system.

As was true for them, so was true for Armenian merchant communities across Eurasia. Armenians were not the only trading diaspora (the book concludes a chapter comparing the Isfahan Armenians to Sephardic Jewish and Multani Indian communities) but they did form an important one that cast a long enough historical shadow to show up in your book.

Sorry if this answer got a little away from me, but there is a very large historical context behind your question. I would be happy to try to answer any follow up questions.