You should only focus on the rocker panels, cuz on the rear the quarterpanel goes deeper (undercut?) then the floorboard, so technically one should simulate that with a piece of tape and spray over that.
The longitudinal (enginebay framerails) should have a bit color from above, due to spraying the enginebay,
Also think the factory painters sprayed with a 45° angel to cover the rockers and bottom of the fenders, rockers, and front and rear splash panels (panels below the bumpers) Someone who has been painting real cars in a factory setting will know for certain