If you play around with a probe at grate level, in the center of your drum you may notice the same thing that I did...... That is, under certain circumstances and loads of meat, the short stem thermometer mounted on the side reads about 40° lower than the readings in the center of the drum. So, you may be cooking hotter than you think if you are only monitoring the temp at the side of the drum.
For different cooks I either use a long stem under-grate therm, or a cable therm.
KCBS - CBJ
Big Green Eggs, Big Drum Smokers, Big Chiefs, Weber Smokey Joe "Custom Tall Boy"
Oil Patch Horizontal
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Barbecue is not rocket surgery