Try closing donw the concave slightly and speeding up the cylender. Most of your separation should take place right at the cylender unless you are overloading it.
I had a 6600 that left 2 to 3 inch cobs in the tank maybe one or two in each hopper. I never found the real cause,but I did discover that if I left the seperator running while unloading it elimated the problem. Seemed to be some place where they bounced through the combine when I would disengage and engage the seperator.Hope this helps. lucky luke