QUOTE(Scremaz)

he basically told me that it didn't work the way we supposed and PXP0 is calculated only incidentally
I've still got a long way to go for full understanding but I perhaps now understand the meaning of this cryptic statement. The PXP0 contribution formula in the wiki is roughly correct as a model, but it's not written the exact same as the game codes it, and more precisely the wiki formula is wrong in several ways. (I mentioned one way last year, base attack values we see are not quantized in increments of 0.0854 as that formula suggests: there can be rapiers with 51.1, some with 51.11, some with 51.12 adb).
I think that the tiny PXP0 contribution to base stats could instead be a bizarre form of very complex rounding in the original game code.
QUOTE(Juggernaut Santa)

it got somewhat confirmed when there was some theory about PxP slightly influencing the stat scaling when forging...that theory said that high PxP slightly hinders stat scaling, but it was so negligible that even a LMax ADB item with the lowest PxP possible still had the same forged adb value as a Peerless...the only thing it influenced was some 0.01 fluctuation on some non-peerlesses...like some shields with 38.45 or 38.46 base block having 51.95 block when forged to 50).
I am one proponent of this theory. However more recently I noted that it matters less than I thought, actually perhaps not mattering at all for attack damage. The two reasons it doesn't matter for attack damage, and the reason someone did see it mattering the tiniest bit on a shield, are:
1) The tiny size of the PXP0 contribution to base stats varies with each stat. It is the tiniest on attack (study the wiki formulas).
2) Attack is unique as a stat because the scaled actual damage value removes the decimals, getting rounded to the nearest 1 damage (50.01 base may do the exact same damage as 50.05 base).
So a forged LMax ADB rapier with the lowest PXP0 might have the same scaled damage as a peerless, or at most it will be 1 damage less which is pathetic.