When using paper towels as substrate in a tub, do i set the thermostat to heat the top of the paper towel to 90 degrees? Or do i set it so that just under the paper towel is at 90? To get the top of my paper towel to 90, i have to set the thermostat to 99, with underneath it measuring at at around 97-98. Worried about her moving the paper towel and being on that. Thanks for any help