Tuning a heat pump vs resistive heat is a much tougher game than it should be. In a moderate climate, I use my ecobee to ensure aux heat doesn't come on until it's below freezing, and it should only come on if something has gone wrong at that point too. Unfortunately, many thermostats by default will use resistive heat in relatively normal scenarios, of worse, when you've programmed home and away times intended for efficiency but disparate enough to activate resistive heat.