That is not typical behaviour for a UTH when the power is off they start to cool immediately. that is the base premise behind a pulse proportional, they cycle many times a second.

The hydrofarms I have tested all run over the temp set. I suspect yours is as well. i tested the original series (3) and then got 6 more of the 'new improved' ones straight from hydrofarm the probe response cycle is a touch faster but past that are the same. The very best on off on the market shut down one over the set point. it is unlikely that hydrofarm has improved this, remember they are made to heat soil, and gel medium for seedlings the overage is likely designed into the unit due to the properties of soil.

With small snakes I personally use a hot spot of 88º and cool of 79º with ambient air of 80º little ones generate heat when digesting and raise the hot hide temp up 2-4 is not uncommon. 91º starts to be a the highest end of ok given this. Big snakes are different 90/80 ambient 78-85º is fine.