The "Ember Girl" instance traces Master Soran's past. In her network of relationships, many people were entangled with mining, and most of them even got hurt because of it.
In the "Residence of the Dead," the phrase "living without a soul" sounds vaguely religious. Normally, an investigation should focus on religion. But this religion is a byproduct of the mining industry—its core is still the mining group. No matter where the final "residence" ends up, it can't be wrong to start the investigation with the mining group.
Both instances are connected to the mining group, but "Residence of the Dead" is more overtly so than "Ember Girl"—the former's direction is even fixed.
The mining group is just one of many possible threads in "Ember Girl," but it's a main participant in "Residence of the Dead," and it very obviously ties the present and the past together, almost as if it's hinting at something.
