I have the same rack (older 3in felxwatt version) and I have my helix set to 105 to get the temps I want. I just got a new one at the last white plains show with a ve-200 thermostat. I'm still playing with it, but I am anticipating needing to put it in the 100-105 range to get a 90 hotspot with cypress mulch substrate. I believe that the need to set it so high is a combination of cool ambient room temps and the fact that the fexwatt doesn't touch the tub directly.