Control to Output gain-phase measurement

[Magnethicc]

Hi everyone.
I want to know if it is possible to measure the control to output transfer function in real life and if yes then how?
In LTSpice I use AC analysis of the small signal model of the DC-DC and then take the ratio of output voltage to error amplifier output.
Lets assume I have a this buck converter (in reality I will have a PSFB converter) - attached

1) In real life I think to inject a signal at point 4 (I have access to this point) and hook the Frequency Response Analyzer (FRA) at Vb and Vout. Is this a good way to measure the control to output transfer function?

2) I would also like to measure the compensator transfer function so I though this time to hook the FRA at FB and Va. again is this a good way to measure the compensator gain?

3) a question about the frequency of the injected signal - can I inject a signal with a frequency of 1/2switching frequency and above and get results of meaning? or after 1/2 switching frequency I will get garbage information?

Any responses and further information is highly appreciated!