Funnel question?

This is in regards to the funnel on the bottom of the feeder just above the spin plate. Is there any reason it needs to be smaller at the bottom vs the top? Could I use a straight 2 inch diameter by 4 inch long piece of pipe? I need to drop the spin plate down another couple of inches.

can't really think of a reason why that wouldn't work as long as the corn drops out ... I have several that are metal about 2 inches in height that are straight wall.

Won't hurt a thing. I have a couple that are straight and no issues.