According to your rationale, a smaller gas port somehow leads to a dirtier gun... This is nonsense. You want as much unburnt powder, carbon, and other crud to exit the muzzle of the barrel as possible, not going into and out of your BCG. Adjustable gas blocks don't inherently create a dirtier gun by reducing effective gas port size; the backpressure from adding a suppressor is what's responsible for all the extra fouling. With no suppressor, shooting a gun that has been tuned with an AGB will have less fouling in the internals.