i just pulled apart my vert head unit (has alpine via P.O.) to install a new one. All stock wiring had been bypassed, but I found that the rear headrest speakers are wired to the 4" under dash speakers (RFosgate punch), left and right. Front door speakers are wired to front, all normal there.
i found this rather odd, any reason this should be done?

 

Guess I'll just play with the speaker wiring and see what I like best