The Power Play stats screen for Li Yong-Rui lists the 15% outfitting price reduction under the heading "Control systems", so naturally I would assume that only control systems have this bonus.
On the other hand I have read somewhere the suggestion to go to the Diaguandri system for outfitting because that's a high tech system that stocks high-level parts. However, Diaguandri is merely an exploited system, not a control system.
So in which of Li Yong-Rui's systems does the outfitting reduction apply? Control systems? Exploited systems? What about the HQ system, Lembava?