Closer the better if thats what you are trying to prevent , I have gotten it following at a save distance as far as safety goes , gives that rock time to get good ,and airborne to nail the windshield , or if lucky just gets the paint real good just above the windshild

Either stay way back , or tailgate to the point where you can't see the rear tires, keep that rock from getting airborne . Then you can use your collision insurance for a complete repair if you ,and the vehicle survive enough for repair.
In all seriousness, sometimes that rock just stays in the air just long enough regardless of what you are doing . I've gotten it on a road thats been chipped , and had the rocks get me from a vehicle coming from the opposite direction going too fast on the repaired road . , two lane road that is . Or passing me on a repaired road when they shouldn't have .