About the blue cardboard, after you close the back cover, the back cover doesn't block the air way (still have a gap), hot air from heatpipe and hdd will exhaust by the cooling fan.

If your HDD is operating, the ambient temperature better around 5-55 degree celcius, IF your room temperature is 50 degree celcius, i give you 1000 fans, you also can not cool it down, you just blow the hot air into the laptop.

Not matter your laptop in what environment temperature, the HDD max temperature is 65 degree celcius.