You want them to be "wider" at the rear (by auger), than the front. {usually about 1/16 to 1/8" wider; at rear)

You want the opening "centered" over snapping rolls.

Marion Calmer suggests setting your initial opening about 1/16" greater than the width of the largest lower node on your cornstalks, out in the field.

Copy and paste = Stripper plate gap should be 1/16” wider than the widest portion of the lower corn stalk nodes.

http://calmercornheads.com/in-the-field/down-corn