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

Some time ago, this issue was discussed here.  The question then was not "whether" VTF goes up when the pivot point is raised, but "how much" does it go up.  Someone did the experiment, and the answer was "not very much", but definitely VTF went UP.  You could repeat the experiment but don't start with VTF =0 as in your model.  Start with a real world situation where VTF is any value >0.  Then you will see VTF go up if pivot is raised.
Also, think of your car sitting on level ground.  It has a given weight distribution between front vs rear wheels.  Think of the front wheel pair as the stylus tip.  Now jack up the rear of the car.  What has happened to the weight distribution?  More of the weight is supported by the front wheels.

lewm,
You must include a pivot in your analogies or they don't apply.  Imagine raising the pivot point until the stylus lifts from the platter.  The arm will balance at less than vertical.  That's because the leverage at the cartridge decreased as the cartridge neared the gravity line and equilibrium was reached (balance).  The VTF is then zero.  It must have decreased.

lewm

... The question then was not "whether" VTF goes up when the pivot point is raised, but "how much" does it go up. Someone did the experiment, and the answer was "not very much", but definitely VTF went UP.

Yes, it goes up, and it's easily measured with a stylus force gauge.

Funny, my experience is the opposite.  I wonder if the answer flip flops depending on which side of parallel the tonearm is.  Above, below or horizontal.  I know what my arm as it's set up does.  Physics isn't my thing and there could be (and most likely are) other explanations I've not considered.  I would love an answer from someone who actually knows.  No one here does, including me.  It's fun and didn't get too sideways.  Cheers!

Thanks guys.  If jcarr catches this thread, maybe he can weigh in with some practical advice since I am using one of his cartridges (Lyra Kleos).  

My sense is that lewm's approach makes the most sense.  I ordered a cheap super light/small bubble-level to double-check the azimuth and VTA one more time.  I will probably tweak the tuchus (the backside) of the arm up a smidge and call it a day.   

While I can envision that raising or lowering the tail of the tonearm will affect VTF and the P-S distance to some degree, I surmise that a small adjustment of the VTA wouldn't make all that much difference in SQ.  I am not OCD about my turntable and do not have the patience to make a minute adjustment to VTA and then readjust the P-S distance and VTF.