I guess I don't get it.
Measurements at those proximities will have little bearing, IMO, on what is heard at the listener position - that is, unless things are REALLY outa phase / time alignment. There is so much sonic/acoustic reaction in the near-field, that to measure things well
inside that field would seem to be ignoring real affects outside that domain. But, I'm confused...
Assuming the engineers/makers had things fairly close, FFT will reveal what is occuring at the listener position and guide your fine tuning.