My SJ5XXX has a Ptone in the middle position, and as far as I know, I'm the first to do it. I changed the wiring (reversed wires with the bridge) so that the Ptone is solo'd at the one position. It has more mids (of course) and more snarl. At home, I keep the bass with the middle solo'd for the cut and the tone.
Actually, Sheldon gave me the idea when I was discussing putting a Ptone in this bass, as he reminded me the middle is more in the P position than the neck PUP is. I still wonder why everyone wants to put a Ptone in the neck position, I personally love the FD3 tone there, and use the neck PUP solo'd a fair amount of time during gigs. It is bassier with a smoother tone. Volume is sixes, for a volume bump during lead solo's, I use the neck/middle in series, or hit my Phat Phuk depending on tonal needs. The middle/bridge combo gets close to a J tone in parallel. It is a bit of a compromise, but is more melodical than the middle/bridge in series. The middle in parallel and bridge in series is even closer to a Jazz tone. I hope this makes sense.
I forgot to mention, the bridge is FDV.