Probably Synuefe XR-H D11-102, as the first discovered and closest known system to the bubble. There's a substantial distance (more than one 40Ly Jump at least) between that and the main body of guardian sites closest to Regor Sector.
Even at the time, a galnet article at the time suggested this was a "perimeter" site, distant from most others, and so validates it's probably the closest by a long way.