Elrick said:
That's part of the dilemma for the pirates. They need to be far enough out from the world that they can get away afterwards without pursuit being too close behind them, but close enough in to maximise their chances of meeting a potential target.
The real problem for pirates (in systems with system defenses) is lurking for any useful length of time in a spot far enough out from the world that they can get away afterwards without pursuit being too close behind them, but close enough in to maximise their chances of meeting a potential target, without arousing suspicion.
Ships on innocent business don't hang about in space. They arrive in the system, switch on transponders, contact system control, get a flight path assigned, and proceed at their optimum speed to the surface, conduct their business, and leave again on an assigned flight path going as quickly as they can to the 100 diameter limit and jump out. The odds that a suitable prize will happen to arrive in the system at precisely the right time are not good (They increase with the size of the population (or rather, the amount of trade, but that correlates to population size), of course, but so does the size of the system defenses). The chance that system control will assign the pirate a flight path that makes it able to chase down a departed merchant is even smaller.
Besides, in order to chase down a ship that departed ahead of you, you need maneuver drives that are more powerful than the prey's. If you want to visit a starport with a ship more suited for piracy than honest merchant activity without conducting legitimate business and be allowed to depart shortly after a laden merchant vessel departs, you'd better be prepared to shell out some hefty bribe money.
Don't forget that the 100 diameters limit is not a point but is all around the world. You might have your pirates on or close to the jump limit (they made a lucky guess about where they might find a target presumably) and still have a patrol vessel also sitting on the 100 diameter limit but partway round the circumference from where the pirates are.
But if system control is doing its job, the patrol vessel is sitting at the spot on the jump limit where the merchant's flight path directs it. Also, a pirate chasing a departing ship risks the merchant risking a jump from inside the 100 diameter limit (but outside the 10 diameter limit, of course). Incoming ships are better prey in that respect, because they have empty tanks.
Hans