The lip is for a better turbulent zone after it, therefore creating more pull of hot air out of the engine bay, IIRC.
It works for me!!!

JasonS 2000 SVT #1119 Go: SHOshop Intake & y-pipe, Brullen exhaust, Eibach springs, EBC TurboGroove rotors, Corbeau seat, TRW 5pt Harness Show: Knauberized, Clear corners