I wonder why Porsche, Subaru, Corvair or even air-cooled VWs didn't build a car with a flat (also called boxer) engine located below the rear seat thus mid engined?
IMO this is as close to the holy grail as you can get.
You get mid engine for better weight distribution. Flat engine allows both a low center of gravity while preserving the useful rear seat.
I guess modern heat insulation materials might block heat transmission as they are able to withstand space shuttle reentry.
Why they never built such a car?
Maybe by the same reason the wheel was not obvious to caveman?