Systems and methods for setting fiber input power for an optical transmission path may include determining an initial modulation format representing a uniform distribution QAM format, the initial modulation format associated with a first fiber input power and a first spectral efficiency, configuring optical transponders to apply probabilistic shaping to the initial modulation format when transmitting traffic over the optical transmission path, the traffic including probabilistically shaped signals with a second spectral efficiency, determining, dependent on the second spectral efficiency, a second fiber input power, and configuring optical amplifiers along the optical transmission path to transmit the traffic comprising the probabilistically shaped signals over the optical transmission path using the second fiber input power. Determining the second fiber input power may include incrementally increasing or decreasing an optimum fiber input power for a reference modulation format or applying an adaptive selection process to dynamically select the second fiber input power.