Might be worth a worth your while to try deaggresive the concave. The P1 systems only had a 7 bar concave and I believe it is rare that that ain't enough. Easiest way for you to give it a try is make up some thicker than ussual concave filler bars. Maybe three,four or more and I think I would place in front of concave. If that works for them conditions you will know what you need to do. There are other ways to prevent the grinding on concave or seperator grate if you find this is helping the situation. It hard to believe the tremendous amount of cross bars these cobs need to get by without breaking compaired to the P1 systems. For the guy with only cob in return he could leave the door open. We have often did that for edible beans. Good luck