I have a digital hygrometer/thermometer measuring the cold side at ambient temps of 77 degrees, https://www.amazon.com/Samshow-Hygrometer-Thermometer-Humidity-Temperature/dp/B01MRV5NTQ/ref=sr_1_18?ie=UTF8&qid=1500560236&sr=8-18&keywords=digital+hygrometer and the probe is located just above the UTH inside of the tub. I would post pictures of setup, but am currently at work.
Seems a little warm, I'm guessing you don't have a gauge on the humidity either.
Samshow Hygrometer Thermometer, Digital Humidity Monitor with Temperature Monitor, Indoor/ Outdoor Thermometer, Probe, Temperature Gauge Humidity Meter Battery Included https://www.amazon.com/dp/B01MRV5NTQ/ref=cm_sw_r_cp_api_Swf1ybQ39N8V5