Long story short get an infrared gun to measure temps. Make sure nothing your snake can get to is much above 90f. This includes right underneath the CHE.
Bps don't need heat mats. They don't have heat mats in the wild so why should they need them in captivity is the way I look at it. And yes your heat mat if you use one should be under the hot hide to make the hot spot.
(If you have the heat mat inside) .Putting heat mats inside the viv is something ALOT of people do so that is YOUR choice and no one else's. I wouldn't personally do it but alot do so again that is your choice.
Also unless you are doing alot to keep your humidity up then it's hard to believe that you have a 100w che on full on aspen substrate with a screen top and have 60% humidity. . . I do not mean any offence by this it just can be difficult to achieve.