Heated Seats question

[DarkStar!]

Can someone with factory heated seats tell me where the heat is concentrated.
Does it come from the bottom cushion like the jaguars or does it heat at the small of the back like the volkswagens? Has anyone installed them after the fact? I'm sure it's just a heating element that slips in between the cushion and the leather, but are the 996's pre-wired both at the seat and at the batwing?

Please advise... Nothing helps my aching lower back more than heat on the way home.

E