Dear Andre,
I would recommending computing RAOs from OpenFAST using a white noise spectrum (WaveMod = 3), as discussed in our ISOPE 2013 paper: nrel.gov/docs/fy13osti/58098.pdf. A MATLAB script (RAO.m) for calculating RAOs based on the approach outlined in this paper is available in my post dated Mar 09, 2018 in the following forum topic: RAO OC3Hywind Turbine.
Increasing the Gamma factor (WavePkShp) does not increase the energy throughout the entire spectrum; rather, increasing the Gamma factor concentrates the energy at the peak-spectral wave period/frequency, reducing the energy at other frequencies. See, e.g., a plot here: researchgate.net/figure/Spe … _308804645.
Best regards,