Thats why i quit using RHPs. I had the same problems. In winter, it works better but in summer, not so much.
I switched to flexwatt and havent looked back. Sure in the winter if it's really cold, i run an oil filled radiator for the room to keep it around 78F.
I was talking to Skip Frye and we both pretty much run the same set up. Only difference is he uses Corrugated wrap for substrate where as i use aspen or ReptiChips.
My boas also dont sit on heat much. I kept a 90F hot spot. Maybe try 86F hot spot. Skip was telling me he keeps his Surinames all at 86F on the belly heat and they use it. And i too kept 90F hot spots and my boas never used it either. I have dropped it to 86F now.
Seems AP cages hold heat so well that the RHP just warms to cool side too while trying to maintain that hot side lol. And i definitely would make sure they have a cooler side to go to. Overheating will do much more damage to them than being a little cold.