Most SOPs call for the officer to stop at least two car-lengths behind the stopped vehicle, but close enough to be able to read the license plate and observe major movements of the occupants. If the stop is on the side of a roadway, the officer angles his front wheels into the direction of traffic. If the cruiser is rear-ended at moderate force, that may be enough to push the car out and away from the officer and the stopped vehicle. But in no case is it advised the officer or the occupants of the stopped car stand between the two vehicles. A high-impact rear-end of the cruiser is likely to injure or kill anyone standing in front of it.
Something that is common procedure is to have the driver exit the car and step to the rear and side if the stopped vehicle has an occupied backseat. That's a judgment call, obviously; a toddler in a car-seat doesn't raise an alarm
but a couple of able-bodied males in the rear seat(s) might.Typically, the officer will never move forward of a line of occupied seats. In other words, if only the front seats are occupied, the officer will stop short of the rear edge of the front window. Something else that's more common now than it was back in the day is for a lone officer to approach on the passenger side if only the front seats of the stopped vehicle are occupied. This presents a problem if an arrest has to be made because the officer will have to reposition back to the dirver's side, but it offers several other advantages.
Just MHO, as always.