The more I've messed with this, the more I'm convinced that ZWO didn't think about low ambient temperature operation, especially with any wind. Since ambient temperature is -6°C, and the fan runs constantly at full speed, the TEC doesn't need to do anything to achieve -4°C.
Short answer is buy a dew heater strap, not ZWO's sticker, and wrap the front of the camera. This insulation alone might be enough to get some TEC load. Turn this heater strap up to achieve a reasonable load on the TEC. The dew heater can draw more than 1A, so power it independently from your camera.
