A method for controlling distribution of crop material to a cleaning sieve of an agricultural combine, for reducing grain loss, including while the combine is tilted sidewardly relative to horizontal, involving controlling the angular orientation of a distributor disposed between a threshing system of the combine and the sieve, for distributing a mat of the crop material onto the sieve evenly across an extent thereof. The angular orientation of the distributor can be set in advance of tilting of the combine, to adjust for a variety of conditions, including uneven outputting of the crop material from the threshing system, and the set orientation can be automatically maintained or actively adjusted to control a desired operating parameter such as grain loss, even as the combine is variously tilted and the angular orientation of the sieve relative to the combine is independently adjusted to maintain the sieve horizontal.