If you shoot at someone from a mountain or a rooftop, you'll get one star, unless it's a cop.
I fired a sniper round just in front of a cop's legs and got two stars. At one or two stars, the trick is mainly to get away from the area in which you fired the shot. Just get out of sight and don't move until it goes away. More than three stars, same thing; it's just much more difficult with the chopper.
No, the cops should not be "psychic" but it's a vast improvement over the kamikaze/zombie cops of the old GTAs, who were just coded to try to go where you were, running off cliffs because you're standing at the base etc. Now they're climbing ladders to rooftops and attacking while you're dealing with the choppers. Tactical response. NPCs actually seem to have brains this time. It makes me look forward to what can be done with the next generation of hardware.