Something I learned when setting up precise temperature control and monitoring for laboratory incubators and ovens is that the temperature inside of any oven will vary WILDLY from place to place.
With no active air stirring, the variations can be absolutely appalling.
And even with a fan-forced or "stirred" oven, you'll be surprised at how much the temperature varies from place to place in the enclosure.
But still, active stirring of the air is required if you want anything like uniform temperatures from place to place in any oven.
So don't be too surprised or quick to blame the calibration of the probes.
When I calibrated and tested the precision probes and measuring systems in lab ovens, I would take the probes out of the ovens, place them in intimate contact with the reference probe, wrap copper wire around the bundle to hold them together and help conduct heat between them, and then put that whole bundle into a "well" in a precision heated block of aluminum and then stuff insulation in behind the bundle to prevent any airflow into the well.
In my custom made temperature calibration gadget, I set it up so I could also fill the calibration "well" with heat transfer oil as well.
Doing that, I could calibrate to within a couple of hundredths of a degree C over a reasonable range.
Then I'd put the probes back into the oven in question, and again see variations of 15 degrees C or more from probe to probe. The lab QC guys would not like this, but when I showed them the logged graphs of the calibrations, they had to just come to terms with how bad the typical, allegedly "precision" fancy laboratory ovens really truly were!
So when I encounter these variations from place to place in a smoker, I don't like it, but I know it's a fact of life. When calibrating a controller, I've wire-wrapped my reference thermometer's probe directly to the controller's probe to make sure I was really truly calibrating the controller and its probe.
Now if the probe isn't positioned in an ideal place to really give it the best "view" of the average temperature in the smoker, then that's a different problem entirely. ;)