Raul, I have more or less done such experiments already. The only way to get any null point on the playing surface of an LP, with the Viv or any other tonearm that has zero headshell offset, is to mount the tonearm with underhang. If you mount the tonearm with "no underhang or overhang", or in other words with the stylus tip over the center of the spindle, your null point is at the spindle, which of course is useless. If you mount the tonearm with overhang, there is also no useable null point. This is how Lofgren et al came to the idea of headshell offset for an overhung tonearm, I would guess. The L-shaped template supplied with the Viv Float tonearm puts the single null point about 90mm from the spindle, or about 2/3 of the distance from the outermost groove to the innermost groove. Interestingly, Dave Slagle predicted that would be about optimal too. I have found that to extract the best performance, the cartridge ought to be mounted using that template. Even a cm difference in mounting (with respect to the distance from the pivot or the stylus to the spindle) places the single null point either on the label or way out on the edge of the LP, and you lose the magic. (Or at least the magic that I hear.)
I agree with Dogberry. The business of extrapolating from VTF to a quantity in "pounds per square inch" said to represent the horrific pressure on an LP groove, is a red herring of the first order.
