Termite mound humidity is kept close to 100% without being wet. The surrounding Savannah environment is normally extremely dry, hot, and quite a hostile environment--since an incubating mother ball python doesn't leave her eggs for 2 months, it seems likely that ball pythons are happy at a near 100% humidity--so long as there is good ventilation and moisture control. Which exactly what you have in a termite mound--excellent ventilation, due to the chimney setups. (termites open and close chimneys to control temperatures). While ball pythons CAN leave a termite mound, it doesn't seem likely there is such a thing as humidity that is too high for them. Their ability to tolerate much lower humidity around 60% is explained by the fact that they often need to make do with rodent burrows when they can't find an unoccupied termite mound with an entrance.

I do think we should consider 60% to be a minimum, not necessarily an ideal. While ball pythons are very hardy, it seems reasonable that they would benefit from similar environmental conditions to those we keep rainbow boas at--ie, high air flow, high humidity. For those who have the means and single pet animals, this type of setup MIGHT prove to be superior.

Considering the range of conditions we see ball pythons thriving in, they're really quite extraordinary when it comes to their adaptability, but there are limits (particularly with temperatures).