Every device I've come across has it set up so that the plastic part should be inserted closest to the floor (horizontal plugs), or closest to the centre of gra

Every device I've come across has it set up so that the plastic part should be inserted closest to the floor (horizontal plugs), or closest to the centre of gravity of the device (vertical plugs). I don't know if this is specced—otherwise it's very interesting that all the manufacturers agreed to this kind of arrangement.