So just an off the wall thought, but according to some calculations from a Kman video the heater in the Model S uses 342Wh when set at 74 degrees and 6.4KWh when set to hi...if you used one of those small car heaters (12V) for your feet (that is usually the only cold part for me) they only use 150Wh...is this a correct assumption that using the smaller heater for feet is better than the cars heater?