They way you describe is fine personally I do not like to use tape inside the enclosure and usually opt for hot melt glue the probe must not move. There are some that as Argentra mentioned will place the probe outside the enclosure but if you have variable room temps this will often generate greatly variable interior temps.

You don't need so much substrate I use just enough on the hot side to absorb any urine say less than 1/2 an inch the temp on the glass is about the same as the substrate temps.

I have never heard of a Royal python maintaining a core temp much beyond 86º. It is understood that temps too high and the snake can not digest food same for too cold. The problem is with higher temps that thermometers typically used in the hobby are not very accurate and often a degree or two off of correct. When higher temps are use say 94 if things are incorrect on the high side it could be getting close to too warm to digest. I usually will not allow my snakes access to temps over 92ºF at any place inside the enclosure.