All correct. Don't worry about the temperature of the mat. Worry about the air temperature inside the box. The mat is supposed to be significantly warmer than ambient so the tortoise can warm up well above ambient when resting on it. This helps keep the gut of a larger tortoise warm on a cold night. When the tortoise's core temp gets warm enough, it will move off of the mat, as it would move out from under a heat lamp when it was smaller, and over to the side where the ambient air temp is hovering around 80 ish. In winter, it is important to add a radiant heat panel over the tortoise, so it is getting heat from above and below, and so the whole box is warm enough. A Kane mat alone won't be enough to maintain an 80-86 degree ambient.
I don't use rheostats on any of my Kane mats. Been using them for decades now. I just run them through a thermostat as described here. They are "on" if the air temp in the box is below the set point of the thermostat, and they are "off" if the air temp is above the set point. I set them for 80 in spring and fall, 86 in winter when the day time highs are below 80, and I unplug the boxes in the heat of summer when day time highs are always around 100 here.
