Hello,
I think there should be an option to toggle ambulance calls close to other emergency service stations, since randomly generating them would be foolish and cause more problems when it comes to getting calls on water and on silly locations.
Implementing my suggestion would spread the missions out a bit, and give my units a little bit more response time - making the game more realistic.
Getting calls two minutes away from the ambulance station isn't realistic, and it's simply too easy.