Space is big. It’s not only wide and long but, but it’s deep, so there’s lots of room to build worlds, sub sectors and even sectors. Since there is no absolute definition of how big a sector might be, you can fit quite a few areas nearby without having to define exactly how big they are. The vagaries of warp travel make it even easier since relatively long stretches between worlds can be covered fairly quickly if the warp route is stable and relatively calm.
The Corvus Cluster lies just galactic “Northeast” of the Farsight Enclaves of Tau Space on the Eastern Fringe. Other sectors in this region include the Vidar, Kiltor, Acteron and Aleph sectors. The Corvus Cluster is directly “north” (counterclockwise to the galactic spin) of the Tau world of Dal’yth.
As such, the Sculptor System (which includes both Hegira and Dar Sai) is “adjacent” to Tau Space in the sense that there is a stable warp route between the systems (which is also being used by the Tau to expand into the Corvus Cluster).
The Corvus Cluster is not to be confused with the Corvus Subsector located in the Ultima Segmentum and the target of the Crusade of Fire.