Val’s referring to these three constellations, circled here (map from DOTLAN):
The lines represent the probable boundaries. Her logic is sound, and it’s likely the best guesstimate we’re gonna get short of poking DZ or an ISD, which I don’t recommend.
But if one were, say, considering relocating to Kor-Azor space, picking a system below the second line would probably be a safe bet.