Things have changed quite a bit in here with the A90 in the last year or so...
Ortofon - whose claim to fame is very high quality control, above anything else - insists that with the arm set parallel and VTF to the recommended 2.3g, VTA will be correctly set (they never claim SRA will be 92 degrees, per se).
I have fought this claim for years by listening and measurements, adjusting the arm up and down, only to come around full circle and endorse their claim by pure listening. It has taken a significant increase in my system's resolution and accuracy to be able to do that, and at the same time, I have proven that my Dino-Lite USB microscope just isn't reliable enough to accurately measure, or I don't know how to measure accurately. Last I used the microscope was this past November or so.
What this also says is that, before, I was simply unwillingly trying to compensate for issues in the system elsewhere - like the arm and phono - rather than truly focusing on IMD reduction (and IMD is at the core of incorrect SRA). So the only true measurement here, for a layman audiophile who does not have an oscilloscope, is to use the Ultimate Analog Test LP's test track 9 discussed in various threads (I think also in here), and focus on IMD reduction that way. Then, with music tracks, the same results can be verified again; in fact, I did this very test one more time this past weekend with the Sheffield Drum Record, and identified the sonic differences one way or another - and once one can identify what to really listen for, then it becomes second nature. But it looks like it takes a lot of patience and experimenation to be able to do that.
The real breakthrough for me, as mentioned in the previous paragraph, was the arm, and specifically, anti-skating There were a number of discussions last year on this, and once this was dialed in and tracking distortion dropped by a wide margin, then it became a lot easier to tell IMD with SRA adjustments. So from my perspective, chalk one up for a high quality "proper arm" in one's analog rig.
I will agree again that THE RIGHT measurements if DONE RIGHT - assuming one has the chops to do them - is the correct way to START this journey, while listening is another critical part as well. But, extremely few of us have that ability to properly measure, which then leaves us with just listening as the only guiding light. The fundamental questions with that are: 1) what am I really, truly listening for; and 2) what other parameters are preventing me from doing it the right way. So I have come to the conclusion that proper cartridge and arm set up are much more difficult than I had originally imagined, involving a significant number of parameters.
Frankly, had I known that Wally Tools can properly measure my cartridge, I would have engaged them. Finally, kudos to Ortofon's high quality bar, at least for their higher end cartridges.
Live and learn...