A concave section for a harvester includes a concave body having an upstream side, a downstream side, a leading end and a trailing end. The concave body defines an arcuate crop engagement face facing radially inwardly. A plurality of crop passage openings are defined through the arcuate crop engagement face. A cover is configured to at least partially cover at least some of the crop passage openings. The cover is carried by the concave body and is movable thereon between at least two different positions to adjust a degree of openness of at least some of the crop passage openings.