The concept of a bode plot with perturbation is ensuring that the perturbation is substantial enough to induce a measurable change while remaining small enough to maintain linearity. The rule of thumb is for each frequency, your perturbation should be large enough to drive a measurable change in the output (considering that SMPS output exhibits ripple, requiring sufficient signal amplitude to overcome it). In high-gain regions, a smaller signal amplitude is anticipated to prevent saturation from overdrive, while in low-gain regions, a higher signal amplitude is expected to induce sufficient change. I normally begin with constant amplitude over all frequency, and review if need reduce or drive more.
Therefore, for instance, when utilizing .bode, the debug option is crucial for me to analyze the perturbating amplitude. Monitoring the time-domain response is highly essential. I have a document that explains what I have learned from working with .bode; you can refer to it for additional information.
Waveform viewer should handle the plot in polar (linear, dB, log) or cartesian (complex number) format. In general, export is not required.
https://forum.qorvo.com/t/frequency-response-analysis-bode-study-guide/15954