A = Moderate ambient air temperature. Ambient below skin temperature. ACH air temperature is below ambient and well below skin temperature.

B = High ambient air temperature. Ambient is apx. equal to skin temperature. ACH air temperature is well below both ambient and skin temperatures.

C = Very high ambient air temperature. Ambient is well above skin temperature. ACH air temperature is further below ambient and below skin temperature. As ambient air temperature rises, ACH COP, (Coefficient of Performance),increases, maintaining a ΔT, or margin of ACH air temperature below ambient and skin temperatures, providing cooling thermal transfer from skin to ACH air up through very high ambient air temperatures.

As ambient air temperature drops, ACH COP drops, reducing ACH air dT below ambient air temperature, tending to prevent overcooling at lower ambient air temps.
Normally, skin temperature rarely varies by more than 1.8 - 2.0º F.