So, given the new map, I've been trying to figure out what goes where. Of Adāta's immediate descendents, Ayāsthi, Mavakhalan, Kozado, and Pencek are already well-situated in particular regions. Æðadě and Aθáta are not - the latter is described as being spoken somewhere in Rathedan, and the former doesn't address the question at all.
Key to the question of figuring out where these two should go, is the fact that Erhadzy is situated a million miles away and we need a plausible way for it to get there. If I'm reading Zhen Lin's description correctly, then we need to arrange for Yhát to be spoken on the eastern coast somewhere below the Eige delta. Complicating this question is the fact that Naidda, Puoni, and Gezoro, and later their descendents, are already in that area. (Perhaps Gezoro has died out by that time, however. Or not.) So Yhát should probably be not too far north - the far SE peninsula looks appropriate.
There are basically two routes to this region: straight east through the Eige valley, or southwest through Tjakori and then east through Xsali. Unfortunately I can't come up with a very good way to make either of these work. Mass migrations just don't seem to happen very much in modern-Earth-like times. This is the best scenario I can offer (please offer a better one, any of you, if you can think of one):
Aθáta, descended largely from the dialects of Hiphago and Radias, came to be spoken in the Tjakori valley and eventually to dominate there. Later, by E'át times, conflict with the Xsali prompted the latter to invade the Tjakori valley once again, deporting thousands upon thousands of residents, resulting in a diaspora of E'át speakers throughout the Xsali empire. Over the next couple generations the E'át speakers tended to congregate in clusters in various points of the Xsali Empire. Most of these clusters later lost their languages in favor of surrounding dominant ones, but one that didn't was on Xsali's far eastern border, on or near the east coast. The variety of E'át spoken there evolved into Yhát. Erhadzy is descended from the Yhát speakers who migrated to Lesan; Öhat, from the Yhát speakers who stayed.
This would let us place Aθáta in Tjakori, and leaves Æðadě and its descendents free to be placed elsewhere. My vote is for Lasomo and perhaps the Nitaze river valley as well. Maybe it could be descended from the variety of Adata originally spoken in Nitaze and Mezaras?