Thanks for asking. I thought about a sketch, flatbed scanner and USB transfer; and I overcame the inertia to finally install the GIMP on this machine.
In front, the stepped plate overhangs the stagnation point for downforce instead of an air dam. The step accelerates the underbody airflow to lower the pressure.
This might be broadly spread over a flat underbody, or channeled into a central jet. See the cowmeat[IIRC] Civic.
The engine air exhaust depends on the shape of the firewall (and front radiator.
) It's a good place to control the airflow through the compartment and/or radiator.
Emphasis on sealed ductwork.