+1 do it by ear. Especially if you have a dual pivot on your vpi arm wand - makes it easy peasy and you don't mess up your vtf every time you adjust it. And also if like me your fozgo stopped working and you don't want to Spring for another one
"Straight" talk
I can't emphasize enough about the importance of proper azimuth. When even a bit off, the result is smearing of soundstage, emphasis of one channel or the other, blurring of lyrics, loss or air around the instruments...etc. If Paul Simon (et al) doesn't sing in his own space exactly between your speakers....better get a Foz.