What angle should I set the VTA on my VPI turntable?


I can't believe after all these years, I am asking such a basic "analogue 101" question, but here it goes. I own a VPI turntable that has a "VTA on the fly" knob.  I thought the best VTA setting was for the arm to be 100% parallel to the record surface.  

However, based on some research, I am not so sure that is correct way to set the arm to achieve optimal VTA and correlatively, optimal SRA.  Not sure, ... but I think I have to raise the pivot side of the arm.

Any advice would be appreciated. 

Thanks.     
bifwynne


 unipivot. and some tonearm style do not perform. well if it's way above the parallel setting.. either compromise. or find a better mounted cart.

I suggest look up all the videos and article by soundsmith Mr Peter and by Mr Michael fremer.. a mixture of accuracy and compromising art it is. 
@lewm, using a USB micoscope to set SRA is very accurate. You take snapshots and measure with a protractor to a reference line that is perfectly horizontal. I use a laser level. The toughest part is holding the microscope fixed in the right position without any wobble. Once you have a microscope stand figured out it is a breeze. 
You set VTA the same on any turntable....it’s not specific to the turntable, but to the cartridge. In general, you want the tonearm parallel to the record...from there, you can tweak it to your liking, cartridge ass down, or tipped forward...generally ass down, more bass and more full, tipped forward, more treble or high frequency detail....I belive you are looking for a stylus rake angle of about 92 degrees. You should also re-check your stylus down force upon adjusting VTA.
I set mine and mostly leave it alone...there are too many variables involved as far as record thickness etc...unless you want to drive yourself nuts and adjust for every record...
Hshifi is conflating SRA (~92 degrees) with VTA (~21-23 degrees). The two are interdependent of course.

Mijo, an analysis of data in the form of photos posted on vinyl asylum (I think) revealed that most “amateurs” draw the lines incorrectly when adjusting SRA with a USB camera. Thus they arrive at incorrect SRA. Personally I take it as the height of anal audiophilia even to try it. But that’s just me.