Done carefully it does not add a great deal of weight and makes the car much more civilized for those that would like to still have some hearing left when they get old, lol! Stock an STI is louder inside than my 72 Datsun was with no interior at all!
Close, lower A pillars are right in front of the front doors, in front of those are the wheel wells
Rear hatch is refering to a wagons rear "door" The other areas are as you described in the question.
Rear floor is in a wagon, cargo area floor.
Rear areas can mean anything behind the rear seat.
Saw it but to dang tired to respond when I did.