An object engaging in free fall from a state of rest accelerates due to gravity. The simplest of kinematic equations was capable of calculating the distance the object would fall through for every interval in time.
The reason was simple. After a certain duration, the object attains terminal velocity. Basically, after this point, its speed of descent remains unchanged. So, those entering and exiting the Comb travelled through the tunnels at terminal velocity.
The immunity coating against air resistance given to the Ravaged Tribesmen existed for as long as they had a Key. For those exiting, even after the Key vanishes from their body, its residue effects remain.
This residue would protect them during their fall. And the amount was calculated to be enough until they reached the surface. Whether it was the tunnel route or the coating, all functioned based on a calculation preprogrammed in the Comb.