Looking at the map in GIMP, the center of the aisle that Lee would have had to pass through was about four feet from where the rifle was found. If Oswald was reaching when he placed the rifle, the distance would have been less than that. It don't know what Walt means by "down four feet".
Walt just went from "down four feet" to "over two feet". Some of this is stuff in his mind that he can picture but can't effectively communicate.
This policeman shows how someone could lean over the row of low-height boxes and place the rifle. Might have put an elbow on top of a box so as to reach the floor.
Looking from West to East. Row nearest to stairway at camera-left. Rifle removed. Tall stacks of pallleted book cartons at camera-right. | | Looking from North to South. Rifle had to be lifted over row of boxes in foreground to be lowered to floor. The boxes there (three at camera-left foreground) were only stacked two-high. |