Just look at the very LOW Angle of that pointer touching the BACK of JFK. Now, place 2 Tall/Wide SS Agents on the (R) running board of the Queen Mary following closely behind the JFK Limo. Those 2 Large SS Agents standing atop the (R) running board makes that Low Angle BACK shot extremely difficult . Plus, Elm St runs DOWNHILL. This places the Queen Mary at a Higher Elevation on Elm St vs the JFK Limo. This is Exactly why when sharpshooters are attempting to replicate shots being fired from the sniper's nest, they NEVER include a closely following car with 2 Tall/Stocky Men standing atop a (R) running board.
On, "The Men Who Killed Kennnedy" (1988) BBC Presentation, a 2nd hand account of shot(s) being fired from the rear on, "the horizontal" was presented. This "horizontal" shot(s) fired theory was supported in, "Unsolved History JFK, Death In Deleay Plaza" (2003). During the Wiegman segment, Wiegman detailed his climbing out of Camera Car #1 and then feeling the "compression" of a bullet on his face.
And of course, Knott Lab Laser SCIENCE has already Proven that the SBT, "IS IMPOSSIBLE". This is SCIENCE vs a lawyer with a pointer and his slick yakety yak. Not a tough choice to make.