He may just want to be closer to the heat. You said it was 87-90 degrees and I think most people look for it to be about 92. You also said when you handle him he curls around you and we are ~98.5 degrees so he may have been trying to soak that in. I would strongly suggest getting an infrared temperature gun. I think they're more accurate and you can shoot it all over the place and get instant readings. Home Depot has a Ryobi for about ~$30 in stock. Or you can get them from any hardware store or reptile supplier online.