What temps are reaaalllyyy prefered by our snakes....?

[BallBuster7653]

So currently I have a new suriname but I have owned all of the large snakes in the past and right now I am struggling with getting this 30 gallon tanks temps right....Yes yes I know to get a tub or vision cage soon but for now I have an overhead light on a timer for lighting and an undertank pad gets to mid 90s on the waarm side on the left then on the right best temps I can get are 75-80 and aas low as 70 at night. My ? is the cool side temps too low? he seems to prefer them. He gos back and forth so all seems well. Hes eating....Everything is going well so far so Im thinking dont fix whats not broken. I also just ordered a large exto terra rock cave for him. Hope its a good size sure it will be good for the enxt year hes only 28" and about 100 grams....Would love some suggestions and other opinions on temps..thanks ll!!!