It's not standardised but it is possible to give an idea of what's going on which covers a substantial part of what different manufacturers are doing and remove much of the speculation. Personally, I find the reverse P more comfortable to play, for a start. There's also something very pleasing about that mixed PJ sound which isn't quite there with a traditionally positioned split P and J. But first, let's do some measuring.
I don't have a Fender P, the closest I have is an old Japanese Yamaha BB1100S. Other traditional P types are a Bass Collection SB311 and an Ibanez SB900. Measuring the distance from the 19th fret to the leading edge of the pickup, we find:
From what I could find digging around, it looks like the Fender P has the leading edge of the E-A coil positioned round 12.5cm from the 19th fret, which would put the D-G coil at around 15.5cm back. Someone be a dear and measure, if you have one. It would be interesting to see if Fender themselves are consistent across USA, Japanese and Mexican models.
Anyway, looking at the reverse P types to hand we see this:
The Charvel appears to be closest to the traditional Fender position but with the coils swapped around. The famous Warwick growl is coming from the pickups being much closer to the bridge than "standard" and the Warwick E string is read almost 5cm closer to the bridge than the Yamaha. It's a much greater difference than, for example, the 60's and 70's Jazz bridge pickup positions. If you think that makes a difference then surely there's more than snake oil?
As for disco and funk, you can do a comparison by listening to the first Chic album, recorded on a P, and the subsequent albums recorded on a Stringray. The leading edge of the Stringray pickup is, what, a little over 17cm from the 19th fret, so the E and A string is being read from even closer to the bridge than a Warwick SS1. Which tone stands out more?