There seems to be a direct correlation between the low point of the heat management plate and the heat build-up in the firebox. I think the original Yoder Wichita probably didn't have a heat management plate, and customers had less flow issues. We can certainly remove the plate, but I paid for it and I want to use it.
I did an analysis using a 6' level to see where the heat build-up would occur at the fire door. The test requires that the pit be perfectly level, because the unit is built with a downward slope towards the grease drain. When the pit is level, the lower shelf is level.
Here's the lower shelf, which is perfectly level:
The test involves placing a 6' level under the heat management plate, and then leveling it to see where it intersects with the fire door. This should approximate where the heat build-up occurs. I did a quick mock-up using this Yoder side view, but I didn't want to rely on this rendering because I wasn't sure how accurate it is, so I tested this on my actual smoker.
From this angle, you can see that I have the level wedged directly under the heat management plate, and held level using some props.
The level is dead center:
... and here is where it aligns with the fire door:
Notice the smoke build-up line on the inside of the fire door. This completely agrees with this test, and demonstrates that the heat build-up is directly relational to the lowest entry point into the cooker. According to this test, at least half of the upper vent opening will always flow outward, which ruins any design calculations that were used to determine the size of the vent cut-outs.