… shooting stance.
Most of the CBS trial shooters were not using the window ledge box as a rifle rest and none were sitting on a box either.
It’s a bit curious about Euins seeing a hand on the trigger guard. Did he mean seeing a “finger” sticking “thru” the trigger?
Otherwise, it’s not clear to me how and entire hand could be seen since it’s on the opposite side of the wooden stock and obscured by the left hand holding the stock (as per the Oswald actor pose.
About the standing Marine pose: It’s kind of difficult to visualize the sequence of the shooter sitting on the box, then standing up for an theoretical early shot at z160 then going into some crouched position between the pipe and the window ledge box and shooting 2more shots fairly accurately at the moving target.
And all 3 shots heard fired by Harold Norman in span of only about 4 secs( as per his video demonstrations)