I have a masonry wood-fired smoker (picture below). It has two shelves for meat - one just above where the hot smoke enters the cooking chamber and the other half way up. I almost always put my meat on the upper shelf. I have long had my temperature sensor about five or six inches above the upper shelf. And as I usually don't have the upper shelf full of meat, I think it has given me pretty good temperature readings for the cooking chamber. In the first picture below the lower section doors are open and the upper shelf is at the base of the half-cicle upper door.
Today I started up the smoker at 9 AM and at noon put 30 lbs. of pork loin on the top shelf - that's three whole pork loins - and they just fit on the upper shelf - they occupy the entire shelf with only small openings for the smoke to migrate through.
I thought about how that might affect the temperature in the upper half of the cooking chamber. So I kept my temperature probe in its usual position above the upper shelf - but added a second probe - dangled it from the door lock to the lower section - so the second probe sits and inch off the inside of the door and about five inches below the upper shelf where all the meat is. The 207 degree reading is from the lower probe (between the firebox and the meat) and the 158 degree reading from the probe above the meat (between the meat and the chimney vent).
WOW - a 50 degree difference between the lower part of the cooking chamber and the upper part. I expected some difference, but not that much! I suspect that as the meat heats up, the difference will be negligible. I also suspect that if I want to keep the smoker at 200 to 210 degrees, I need to be watching the second probe that is in the lower section of the cooking chamber.
Just thought this might be of value to some.