Curiously, according to this site
http://www.feldoncentral.com/bbqcalculator.html that calculates smoker dimensions, my OC Wrangler has a firebox that is 180% of their recommended size for a firebox based on the length and diameter of the cook chamber, and the chimney pipe is quite a bit longer than their recommendation of 10.75" length (mine is 23" long at the center line including the elbow)...
They also recommend that the area of the opening between the fire box and cook chamber be 40.83 square inches - my OC Wrangler has an opening area of 32.24 square inches - 78.9%.
Lastly, the firebox intake is almost spot-on with their recommendation with the firebox door closed and the 9" diameter damper fully open - 15.31 square inches.
So, according to them, the firebox is too large, the chimney is too long, and the firebox to cook chamber opening is too small...
I have no clue how accurate or useful the recommended calculations are, but its interesting.