a threshing system;

a sieve positioned and configured for receiving crop material containing grain from the threshing system and allowing the grain and smaller elements of the crop material to pass through the sieve while guiding and propelling a flow of larger elements of the crop material past an edge of the sieve;

apparatus in connection with the sieve, including a first actuator configured and controllably operable for positioning the sieve within a range of angular orientations with respect to a reference;

at least two grain loss sensor sensors disposed adjacent opposite ends of the rear edge, the sensors configured and operable for sensing information representative of a quantity of the grain present in the flow of the larger elements of the crop material past the edge of the sieve, and outputting signals representative thereof;

a crop material distributor disposed between the threshing system and the sieve, configured and operable for distributing the crop material from the threshing system onto the sieve;

apparatus in connection with the crop material distributor, including a second actuator configured and controllably operable for positioning the distributor within a range of angular orientations with respect to a reference, independent of the angular orientation of the sieve; and

a control system connected in operative control of the second actuator, and to the grain loss sensor for receiving the signals outputted thereby, wherein the control system is automatically operable for controlling the second actuator for positioning the distributor at different angular orientations, for minimizing the quantity of the grain in the flow past the edge of the sieve, wherein the control system automatically controls the angular orientation of the distributor as a function of a comparison of the signals from the at least two grain loss sensors, wherein grain loss from one side of the distributor exceeds the grain loss from the other side by a measured amount.