The system and method automatically controls the position of at least one deck plate of a harvesting unit of a corn header so as to increase the width of a stalk receiving channel or reduce pinching forces between the plates when entering a stand of corn to facilitate alignment with the corn rows, and to change the position after a suitable time period or other condition or event, to narrow the channel width and/or increase pinching force, to reduce kernel loss while also monitoring forces exerted against the plates by the stalks and responsively adjusting the plate position for maintaining a desired force on the stalks or width.