I bought a reptitemp rheostat (20 bucks) from petsmart and have both my heat pads plugged into it. However turning the control button from low to high doesnt realy seem to do anything, I pluged a lamp into it to see if it was working, and I did see the lightbulb dima bit when set on low and brighten a bit when set to high ( just a bit ) so I dont understand why its not effecting temp control in my enclosure as drasticaly as I thought it would. Are these rheostats only supposed to fine tune heat by a few degrees.