if you stand over the jack handle you can position yourself such that it can hit you in the head.
if you move off to one side slightly and then kneel down so you are pulling the lever down towards your head the way your arms will move if you keep both hands on the handle will stop you from being able to position your head above the handle.
if you go down onto one knee you are positioned with one foot in front of you towards the vehicle so if something begins to go wrong when you have a panic reaction you are already moving away from the danger.

