Yea 90* for the uth is good. Make sure thats UNDER the substrate. So you put ur thermometer probe under the substrate(keep in mind its the thermometer probe not tstat probe) if you have the temp at 85 there is some degrees lost between the uth and the top of the substrate where he is so i would raise it a bit. Also try to bump ur humidity up a bit if u can keep it at constant 50-60%