The third and fourth show the mandibles below the chin. Skin elasticity I addressed.
I'd say the eyes are a more significant difference between the two, especially the brow. But we're comparing a static model to a dynamic mask.
As for positioning, Scar's mandibles are capable of the correct position and BTS shots show similar posing (especially static stunt masks).
His shape isn't really the problem, it's how he was animated.