We really do not know how far into the Deep Periphery the Foxes have been traveling. First, they are a bit closer than I think folks are using- the Chainelains are a big blob on the maps i have seen and that is a private Fox preserve. Who knows how far beyond that they have been building up?
Second, the Foxes were trading with the Hansa before the Reavings so they are willing to travel a distance to make contact. They were selling the Hansa some of the same exact stuff they were selling the IS powers- specifically a Ha Otoko! What could the Hansa give that they could not get cheaper closer to home?
Third, ISP is being used as a factual source for the Imperio's position and attitude? IIRC the ISP series are widely known to be rumor collections- some things they say are absolutely true, some of the fabrications are based on a shred of truth, and some are outright tall tales. If IE found a stable base for jumping off points for expeditions into the very deep periphery for their treasure hunts are they really going to make the truth known? Or is it in their interest to tell everyone else the Imperio is under threat of invasion, xenophobic, and a collection of poor dirt farmers?
Sure, the Scorpions/Hellions have some problems- not denying that at all. But they also have some solutions, and while the Imperio likely has more to gain in a trade relationship with the Foxes than the Fox merchants do that gives the Fox merchants a degree of control they are sure to like. After all, the Imperio very likely has the option to trade with Jarnfolk, Hansa or Foxes- and the Foxes are the only ones who operate from a tech base the Imperio is going to want to acquire.