I'm having temp problems and need advice

[Bogertophis]

Also, this picture shows to put the thermometer probe under the substrate. Is that necessary and what is the reason for doing that since the thermostat probe is already practically right there.

To make sure that if, or more likely, when- your snake pushes the substrate aside or decides to burrow under it, they cannot come in contact with excessive heat from the UTH. Perhaps because they are heavier-bodied snakes & take a while to warm up (?), ball pythons seem oblivious when it's too warm until they've already suffered a thermal burn. BPs are also notorious for staying in one place for long periods of time, so that behavior also puts them at higher risk. It's just better to prevent injuries (pain & suffering) than try to fix them later (cost of vet care + uncertain outcome).

The thermostat tells you what the UTH is set for & trying to do...the thermometer tells you what it's actually accomplishing where the snake is. Never take the thermostat's "word for it".