I was reviewing some past threads and I noticed the one by 8820patrick regarding concave clearance in corn. I have a 6620 Put a new concave in last year and zeroed to factory specs. 1/4" at second rasp bar in front and 1/8" in the rear inspection opening. Had the same problem with cobs in sample. However, doing great in beans. Never had the problem prior to new concave. Do I need to open up the back in corn? If so should set in back in beans?