Would it make any sense to have stipper to very rear of and inbetween deck plates up flush with round bar on deck plates. Try adjust average speed of head to land cobs at rear of deck plates. This could create larger surface for cob to come against and stop kernals from trickleing forward. I believe I've heard that squareing off round stock or tacking on thin flat iron may help. I like a ledge on top of deck plates for I believe they keep the kernals from falling between but they maybe should be flater. If any of this makes any sense you could give it a try on a row or two. Best of luck