Combines centering concaves to rot or 1680

I assume you have concaves with extensions bolted to the left side. Ignore the extension and start counting bars from the left side (the outside of the concave is the zero bar). Your rotor should come closest to the 7th bar for best threshing. The easiest way to check is to temporarily adjust the stops to let the rotor barely make contact, then spin it by hand with the center concave removed so you can watch both the front and rear concave closely.

i would try setting your pinch point a little further up on the concaves, try for somwhere between the fourth and sixth bar. (not including the extension)