I wanted to add something I noticed roasting today..
I installed a MET Probe a few roasts back and read Temps should stay below 450*

Anyway I noticed while increasing air after drying my ROR stated gaining so fan was not high enough and had more heat stored in burner chamber than air was pushing out..

I see my low fan speed should be higher than slowest speed so chamber is not warming more than air is removing..

Is this theory right or am I missing something..

Air pushes out as much heat as burner adds, not burner chamber gets hotter and heat increases when more fan is added....

My experience is similar with perforated drum but less fan is needed than you describe.

I think if air/gas is set right your ROR will not rise if fan is increased.. IMHO it will stay the same or lower..