Raul. You have no idea what my background and understanding is.
What I do know and understand from many years of experience, is you are delusional if you think you are accurately measuring differences between .01 and .012 dB, and even more delusional if you believe that your RIAA is accurate to that degree from 20-20KHz
The fact that are even trying to achieve that tells me that you are indeed chasing numbers. I recommend hanging out at Audio Science Review where all that matters is numbers. You will be as happy there as I am every time I spin a record through my .6 dB phono corrector
P.S. My apologies to the OP.. I am done with this distraction, Get a good MM stage with high input impedance and a quality SUT and you will be as happy as I am in my .6dB world