Straw chopper counter knife bar with blade between concave and knife bar pivot

An agricultural harvester machine comprising:

• a chassis configured for movement on a surface;
• and
• a residue chopper comprising:
• a cutting chamber housing defining a cutting chamber therein;
• a plurality of cutting knives mounted to rotate along a cutting direction within the cutting chamber about a cutting knife rotation axis;
• a counterknife shaft unit mounted at a fixed location relative to an outer surface of the cutting chamber housing, wherein the counterknife shaft unit is rotatable about a counterknife shaft rotation axis through a range of motion between a first position and a second position, and wherein the counterknife shaft rotation axis extends parallel to the cutting knife rotation axis;
• an outer face defined by a portion of the counterknife shaft unit;
• one or more counterknives secured to the counterknife shaft unit and extending radially outward from the outer face, wherein the one or more counterknives are spaced a first distance from the cutting knife rotation axis when the counterknife shaft unit is in the first position, and a second distance from the cutting knife rotation axis when the counterknife shaft unit is in the second position, and the second distance is less than the first distance;
• wherein:
• the outer face and the outer surface of the cutting chamber housing define a trailing area located between a first line extending between the cutting knife rotation axis and the counterknife shaft rotation axis, and a second line that is parallel to the first line and spaced from the first line along a tangent to the cutting direction, and
• the outer face is configured such that a gap distance, as measured parallel to the first line, between the outer face and the outer surface of the cutting chamber housing at all locations within the trailing area remains constant or increases in size as the counterknife shaft unit is rotated from the first position to the second position.