Oswald did not shoot while seated on the box away from the window: He had to be right at the window in order to be seen from the street by Brennan & Euins while taking a knee and firing downrange.
Images are from Stephen King's '11.22.63'
Oswald is played by Daniel Webber
Oswald awaits the motorcade
Oswald reacts to motorcade arrival at Houston
Oswald takes a knee and tracks Kennedy at SN window