No Warping Zone: You could, in theory, put a wormhole pair anywhere you liked – high mass notwithstanding. The traditional location out on the edge of star systems has more to do with size, ease of construction and transport, accessibility and defensibility, and minimizing the consequences of their extremely explosive, if mostly theoretical, failure mode if something should go Horribly Wrong than any sort of physics-derived limitation.
Putting a mouth close to a populated world might be physically possible, but it turns the endpoint into both a port and a strategic vulnerability. The outer-system convention reads less like a travel limitation and more like deliberate infrastructure policy.