Mea culpa.
I was still bothered by the difference I had between my sweeps and MLS measurements so I reviewed all my measurement chain and dig-up a little bit more.
This post on gearslutz forum putted me on the right track.
For all my measurement my mic was pointing at the ceiling (vertically) at 90 degree instead of pointing horizentaly at 0 degree. According to
this other post on minidsp forum difference can be relatively subtle at high frequency (~ 2dB).
I've re-done 4 measurements. 2 with mic at 90 degree using both signals and 2 at 0 degree again with both signals. the aproximatively 2dB difference was true with sweep signal but far more with MLS.
Turns out MLS signal is more sentive to mic orientation than Sweep. MLS and sweep signal at 0 degree matched perfectly except a subtle difference at lower frequencies around 40Hz.
I just lost my PHD of surgery :-( but now I know tha my mic (an Apex 220, I don't know if mentioned it before) is a "Free field mic".
For me, trying to correct listenning area with only one point measurement is like trying to analyse annual sales records by looking only the sales of July. So I've re-done the "9 points dirac live sofa measurements" (no shorter name yet) using sweep with mic at 0 degree and time aligned impulses at the higher positive peak.
Sorry but now that I finally resolve my high frequencies issue (it took me more than 60 seconds this time) I maintain my statement, Vector average is far more better for frequencies correction. Never done phase correction so far.
One question. With wich filter do you sirs deal with room mode ? For now, I use lowshelf filter at 100Hz to minimize it but maybe you now better solution that don't include using wall bass trap.