A transition cone for a threshing system of an agricultural harvesting machine has an inner surface with a tapering inner circumference between a wider upstream end and a narrower downstream end, and a plurality of vanes in the transition cone. Each vane extends between the upstream end and the downstream end and at least partly around the tapering inner circumference. Each vane includes an upstanding segment extending away from the inner surface, and a base segment extending from the upstanding segment along the inner surface on the downstream side of the upstanding segment. The base segment has a thicker proximal region adjacent the upstanding segment and a thinner distal edge opposite thereto, with a curved exposed surface extending there between.
