All crews are stationed, either in a ship or a habitat. Crews that are stationed at a habitat gain an additional bonus of up to 20% to their overall efficiency. However, this efficiency bonus diminishes, and even turns negative (to a maximum of -25%) as the population of the habitat exceeds the soft cap.
Implementation:
Subtract the population cap from the current habitat population and divide by the cap:
PopRatio = min(max((Pop - Cap) / Cap, 0), 1)
Multiply by the difference between the efficiency and global minimum, and add back the global minimum:
StationEff = PopRatio * (Eff - MinEff) + MinEff