Were are you takeing measurements for your day time temp and how? You don't want the soil to be that warm, its your ambient air temp you want at 84f. And to be honest like Jason mentioned before it doesn't need to really be that high, 84f to 85 is the highest that is recommended. A lot of care sheets and people that keep them will say anywhere in between 80f to 85f is were there day time temps should be. I keep all mine at 82 during the day then let it drop down to 77f at night, I used to keep it at 79f but changed it to 77 awhile back. Keeping them at this temp has had no ill effects and they eat and poop like they should and they are pretty big frogs. I know the heat is very important but I think you may be overthinking it and giving yourself headaches for nothing, I would never give you advice that I thought would put your frogs health at risk. Out of all honesty if you can get your daytime air to 82f or 83f your frog will be ok. And ya I know Ants Canada, I had lots of email conversations with him and learned a lot about different species from him. He knows his stuff that's for sure.