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[SlothHead]

You should position the probe where you want to control the temperature, which should always be the hottest point in the tank.

So, you will want the probe to be in the basking position of the snake. This way you know that they basking position will be a certain temperature and no more. And therefore the rest of the tank will be cooler than this point.

Try not to have your basking position directly on the floor either, try and have it off the floor closer to the light. This will alow for a smaller wattage heating globe, and greater control of the enclosure.

Couple of problems putting it in other areas.

Putting it in the cool end, as prior mentioned means that you will get the heated area stabilising at the cool end temp on days due to ambient temps.

The problem with having it in the middle is that you arent going to be getting much of a differnet in temp from one end to the other.

So i would recommend using a lower wattage lamp, or a ceramic, and building the basking area higher off the floor. Then position the probe basically right there. This gives total control on the basking area which is the important bit, and so long as you have the ventilation set properly you will get an excellent gradient

Hope this helps

What size enclosure are you trying to run and what animal?