Recent discussions regarding the sniper (possibly awkwardly) standing versus sitting or kneeling for an early shot taken about 9 seconds before Z133 (Z124H) prompted me to use my 3D model to test a sitting positon similar to my Z223 model. I found that a slight rotation at the waist of about 5 degrees along with head, neck and arm adjustments allows a smooth transisiton through Z124H to Z223 and Z313 positions. Attached are four views from Z124H - Z223 including the models point of view from his left eye.
I think you meant to say, "About 9 seconds before Z313," not Z133.
Regardless, was the window really open that much?