I actually did a term paper on this in my Physics in Sports class in college. What controls amplitude in arm throws and suplexes is linear velocity and angular velocity, both are employed in different stages of these throws. basically it means the taller you are, the more amplitude you can get. This is why little kids cannot hit high amplitude throws. They simply arent tall enough to generate the right amount of velocity in these moves. Watch the clips below. One kid is 5'4'', Mike Foy is 6'4". Mike doesnt sit at all and you can see, they both do the same move and one is super high amplitude, one isnt.
Starts at 2:11