The documentation that BPs are apparently more sensitive to heat (in the sense of being more aware of it) on their dorsal saide as opposed to their ventral side has already been posted on this thread by Rabernet. It is a quote from the book by the Barkers, in other words, VPI, in other words, some people who have a lot of experience with BPs, and a lot of contact with a lot of other people with a lot of experience with BPs. Admittedly, it is anecdotal evidence, not the same as a scientific study, but when you have a large body of anecdotal evidence, and it all points in one direction, that makes a very strong case.

I agree with The Mad Nucleus when he (?) said that Little Indian Girl's argument about the temperatures in the wild didn't quite make sense. How the ground gets warm does not matter; what BPs experience in the wild is that at least some of the time, the ground is warm. I'm not going to pretend to be an expert on that specific region and say exactly how hot it is or how much it might vary, but generally the ground is an excellent thermoregulating device in the sense that it absorbs heat and holds it, so it changes temperature slowly. Animals that live in burrows will have much more stable temperatures than are at the surface. Also, when temperatures drop at night, the air temp will drop much more quickly than the ground temp, so even the animals on the surface will have warmth below them, and for snakes that means warmth on their bellies.

Mad Nucleus's reply had at least one hole in it as well. True, the hood of a black car can get much warmer than the air around it on a hot sunny day. But how many black car hoods will BPs come across in the wild? The ground in a BPs natural habitat probably doesn't get hot enough to burn them very often. If the ground is that hot, it would most likely be when the sun is shining directly on it, so any BP on that surface will be able to detect that they are getting too hot from the sunlight hitting their back. So it does make perfect sense based on the conditions that BPs are likely to encounter in the wild would have allowed them to evolve to become aware of burning hot temperatures and the need to move to a cooler place based only on what they sense on their dorsal side. They are mostly nocturnal, so when they do come out, the ground will not be burning hot from direct sunlight anyway.