Do you folks with Inkbirds probe the air temperature or the beer temperature? I imagine in a small sealed chamber like a fridge the air will change temperature quite a lot faster than the beer (due to thermal mass as mentioned above). So with the probe in the air I expect the Inkbird will be switching on and off much more often than if it is in contact with the beer and possibly the beer temperature lags behind air temperature by an hour or more.
I have a ~20cm thermowell in the lid of one of my fermenters. It's okay for a cheapo thermometer I've got, but it's not a big enough bore for the Inkbird probe. Currently I don't have a fridge (as it rarely gets over 20C where I ferment and we're going into winter anyway), so taking air temperature is pretty useless - was planning to get another larger thermowell and use that, then add a cheap fridge to the setup at some stage.