I think Hill took the position he was protecting both. Jackie was wrong, he didnt lay on them, they were already down. Then again, Jackie never remembered climbing out on the trunk to grab a piece of JFKs skull. Its conceivable the Curry car and limo stopped briefly side by side under the security of the overpass as word was quickly passed to Curry that JFK was indeed hit by the fire. Im not sure any of the film or pictures show that very brief stoppage.