I usually only attempt the ken combo when I'm high above the stage, so i can afford to use down A, in fact, I like fast falling it, i think it looks cooler lol. but if you know how to use tilt attacks, i dont see why fast falling should be a problem. if you use the same pressure as when you use a tilt, you won't fast fall.
anyway, they way i hold the controller is weird, so sometimes when i try to c stick down, i accidently do a bair or something...so I've just trained myself to use A for uairs and dairs