Heat pumps will only give around a 25-30 degree temperature difference between the inlet and outlet temperatures when the electric heat strips are off. The electric heat strips can be energized a couple of different ways, if the unit is running and the heat strips are needed the auxillary light will come on. When the heat pump is in defrost the heat strips kick in automatically to provide heat while the unit is defrosting. When the heat pump kicks off all together and only the heat strips come on generally this will trun on the emergency heat.
When you increase your setting on your thermostat you are kicking in the second stage of heat, and this turns on the electric heat strips as auxillary heat. If the temperature drops considerably outside the auxillary heat may be needed as the unit becomes less efficient in lower temperatures.