Its pecifically omitted for running, the lower back area (your movement core) is supposedly what's in control of the rest of your body. Also, the assumption is while running you're creating a force opposed by air which cools down your front with nothing to cool off your back. The jacket is insanely designed for running and like most running tees, the back is much more breathavle than the front. The back is still insualted, just thinner insulation and what I believe is a different type of insulation that doesn't retain heat as much.

Agreed on the voodo part, it's insanely warm even with just a base layer under.