Holey Kr@p.... I forgot the width of the RF plate.....
Sooooo, back to the circle calculator..... Set the radius at 12.625" and the segment height at 8"...... Then Chord AB calculates 23.5".... That should be the distance across the smoker at the top of the football..... If the RF plate stops 5" from the end of the smoker, 5 X 23.5 = 118".... perfect for the end of the RF plate for good air flow... Remember, the air has to take a 180 degree turn down there...
Sooooooooo, now that your smoker calculations woke me up, because I had a brain lapse earlier, I think I will go say good morning to my chickens..... (I should probably add that tricky part, about the football shaped opening, in the calculation)