Yamaha Generator question

I only have a single 9610 to gather data from and am taking the risk of making a general statement from it. Posts over the years from other members confirm what I see at a circumstantial evidence level. The spec I see on the PD web page is "Input voltage tolerance", not "Minimum voltage for full output" or something similar. Maybe it's stated elsewhere that I haven't seen. What I've seen for myself is that the 9160 needs a 120 volt or higher sine wave to achieve its rated output. Like a conventional microwave oven, it appears to rely mostly on the peak voltage of the input power. If the sine wave is below 120 volts RMS, or the waveform is flattened as happens with many conventional generators, the peak input voltage is too low for maximum DC output. This is opposite of a WFCO converter that (when it's working) provides its full DC output when driven by lower voltages and/or lousy waveforms.