Good Morning Mr. Wes,
I agree with all the above replies and think first I would experiment with fuel in different shapes and sizes .
Some of the stages that happen in the hopper seem to be wet and slippery wood in the upper levels . On down where the heart is greater it seems the wood start to bake, form a crust and seem to adhere to all other surfaces . Just a little deeper and closer to the fire tube it begins to burn .
On the funneled shape the fist opportunity for the wood to get a toe hold to bring on bridging is the top of the top of the burn tube , but at this point the heat is enough to burn the wood. I think with the bowel design the wood might be finding a toe hold just before the heat is high enough to burn the wood.
One other thing to consider on the rose peddle type funnel it is flexible . Road condition and vibration may be letting the wood spring around enough that during the baking mode the wood don’t have the opportunity to bond .
As I mention above I think I would experiment with different fuel first. If no luck I would split the bottom of the bowel some where it would cause a spring board or flex.