Dude, the cloud of ejected tissue material doesn't fly along with the car hovering over the President. The car is in motion moving forward, the motorcycle cop behind it is in motion moving forward. He will ride into the cloud of material immediately afterwards.
Dude, the limo was barely moving at the time of impact. The officer testified that he was splattered with the material blown backward, not that he drove into it. With the the car barely moving, the heavier tissue would not hang in the air long enough for the cop to ride into it. Gravity was at play that day in Dealey Plaza. Watch the Zapruder film and apply physics......