Ferm Chamber Temp Probe Placement

Got a hold of a used upright fridge and I am planning on using it for a ferm chamber. I got a Johnson digital temperature controller for it. My question how much difference is there as to where to I place the temp probe. Bottom would be coldest and top would be warmest I assume. Would the middle be ideal. I can place three fermentation buckets in the fridge so I think an average reading would be best. Any suggestions, or I am thinking about it too hard?

Thanks in advance, Kazi

Lots of opinions on this. Probe in a glass of water or other liquid, in the air, taped to a fermentor, ...

My keezer has the probe in the air with a fan circulating inside (and over the probe) and it works quite well -- but it's not trying to control fermentation.

Tape it to the side of the fermentation vessel and insulate it. This way it is controlling the actual fermentation temp.

I also tape mine to the carboy with the active fermentation. I don't bother insulating it, unless you consider duct tape insulation...