you mentioned that it is a new tank. I would ask how big his old tank was? What may be happening is if the he/she is used to being in a smaller enclosure where the heat and cool sides are very close it may not realize that there is a warm side now. any time I have had a smaller animal in a larger tank and they consistantly stay on one side I will physically move them over to the other side and keep a eye on them. balls will self regulate there heat if they are in good health, meaning if they are to hot they will look for cool and vice versa. i would agree with the above post about your temps so just show him/her that there is another side to its new enclosure.