Putting the temperature probe in a thermowell inside the beer has a problem: the outside air must get much colder than you want before the probe in the middle of the beer registers cold enough to turn off the freezer. Then all the cold air continues to cool your beer well below the temperature you wanted.
Do as Denny suggests, and make sure that the temperature probe is reading the temperature of the fermenter and not the air by taping it solidly to the conical and putting insulation outside it to isolate it from the air. Putting in a small fan to circulate the air may also help to give better heat transfer from air to fermenter.
To date, this has not been an issue. We have the probe sealed in the thermowell with masking tape, so to prevent chilled air from the freezer entering the thermowell. Thus the reading we get is actual beer temp.
The differential between beer temp vs. freezer is 1 degree or less.
The Inkbird controller is so cool! We have it programmed to maintain the beer temp at +/- 1 degree from our set temp. And we have a compressor delay programmed in so it won't be continuously cycling on/off.
Once the beer temp stabilized at our desired setting (49 degrees F), the actual freezer temp has not varied by more than one degree. We have been watching it very closely, and it is spot on.