Snakes a weird dont try to understand them!!! I honestly belive they like cooler sides and will only sit on hot side to digest During winter the sit in middle of bin (ambient are low like 75ish +/-)
But during summer when it is naturally warmer, 80-82.. They are ALWAYS on the coolside.\
Also im not sure, but looking at that picture that MAY be a little to wet or damp on the substrate! Let it dry out a little (Maybe its just the pic) You dont want to be able to squeeze water out of the coco husk,