I got no dog in this fight, but do recall reading or discussing something about this awhile back, and it goes a little something like this:
"At first, the smoker will have different temps in different locations, but over time, everything will stabilize and the same temps will exist throughout."
TIME is the thing that saves the day. So 1 butt or 10, the cooker's temp will be the same because you'll necessarily be giving it enough time to stabilize.
P.S. Don't maybe slap fridge-cold meat in the thing. It'll make it harder to come back up to temp.