They just spawn where it fits.. And their cars is the best cars ever- when I drive on the high way with my fully modded Coquette, they catch up on me and bumps me so hard sometimes that my car spin. BUT!! When I steal a cop car, it's just a medium/slow car..
they do have a bit of a hard time keeping up with my upgraded f620
Depends on how many stars you have, at least it does for me. With one or two stars, they usually can't catch up, but with three stars they have like a switch turbo that turns on..