Normally fire basket sits on the bottom center, fresh air is blown to it from 3 directions.
Only small portion of fresh air is used in combustion. Most fresh air by passes to flue.
It simply lowers burning efficiency and creats more convention.
More convention simply make meat more tough or more rubber alike.
Indeed there is already perfect "fire basket", the design of Kamado.
Why do not we adopt Kamado burning method to UDS.
Fire basket sits inside the ash box.
Fresh air is blown from side of ash box via air pipe.
the umbrella prevents grease from falling to fire basket to avoid grease fire.
I built this UDS, height 17.7" and Diameter 17.7".
I burnt 1.5 lbs lump charcoal, which kept the UDS at 230+F for 10 hours.
Indeed I "pirate" fire basket design from Kamado, there is not any patent.
You can use the design too when you DIY an UDS.
Hope all we can share the experience