Where to place the probes?

[Slither Seeker]

I've looked at care sheets and spent a little time with a probe on a few vivariums and it has become clear that the temperature gradient that is referred to of 80-90f is a bit ambiguous because it's so relative to position. Leading up to creating a vivarium for our BP's, I have gotten some experience from making a fish tank/BRB vivarium combo two years ago, as well as successfully making a DIY incubator using a cooler, a UTH on a pane of glass and other spare parts. In each of these endeavors, the question of where to place the temperature probe has always come up and here I am again. In a tank without a circulation fan, thermoclines form. So far it appears that BP's spend virtually all their days sitting inside a hide, close to the ground and that is where I should place my probe, about mid point of their body or straight on the ground but I am curious about what others do. So far, it appears that you don't want any place within the vivarium to go below 75f, that's the bottom line at the lowest point, right? Does this mean I do not need to worry if the upper thermocline above where the BP hangs out goes above 90? questions, questions, so many questions. thanks for your time!