I can detect nothing about Secret Service Agent Glen Bennett's position from the Z-153 frame. The image is too small and blurry to decipher anything about his position.
Can you see the oblong-shaped, kinda vertically aligned flesh-colored object about the size of a football in the passenger's side back-seat of the Secret Service Follow-up car in Z-150 and Z-153?
Hint: That's Glen Bennett's face, and it's leaning much farther over to his right in Z-153 than it was in Z-150.
Why?
Because he was trying to see around Dave Powers in front of him to see if JFK was okay after Oswald's first, missing-everything, shot, at "Z-124," half-a-second before Zapruder resumed filming at Z-133.
PS Note that Secret Service Agent George Hickey, opposite Bennett in the back seat, leaned over the side of the car and looked down at the pavement (he evidently thought a firecracker had exploded there), in Z-150 and especially in Z-153.