There is indeed “some” influence between the diameter and length vs the amount of power to be generated.
size and position of the nozzle included.
The biggest role however, in making good charcoal gas, besides good fuel, is the filter setup ( the topic )
The less “drag” your “filter” creates, the more easy the system can “breathe” the more gas can be conveyed to your engine.
I will try to extract some data to compare from my research material and post it here.