Gotcha....
When received my PBC originally - I was really concerned about that opening. And - if you are trying to slow down the cooking process, you can close it down a bit and check the mep impact, and adjust down further if needed.
BUT - I have not known that to be an issue for any of us. To the contrary - The temp. range we seem to all enjoy - is
hotter not cooler..
SO, if anything - you may want to open the air intake shutter ( check the term...I don't remember what it is actually called
) - And - either crack the lid open earlier in the cooking cycle, or leave out one of the two rebar rods, if they are not both being used during the cook.
That will increase the air flow
thru the cooker, offering more oxygen tot eh charcoal, and increasing the temperature. You will cook hotter, and increase the burn efficiency of your charcoal bed. That will leave yo with fewer "old maids" and - faster cook times.
The PBC is very unique because it has made us ware of a gap in the old descriptions of cookers. We used to think of a cooker as either a "low and slow" cooker for smoking , or a grill for fast, hot cooks. (The advent of pellet grills increased the flexibility available to us in one unit. )
But - the PBC is the one cooker that I know of that was designed for cooking
in between low and slow - and grilling. It has been called a "power cooker".
It's simplicity can be overwhelming - if we use pre-conceived notions about how it works - based on other cookers...
Once you get comfortable with it's differences from other cookers - you will be amazed, and overjoyed with your PBC.