Basically if you are on the flats on Orange County - Garden Grove, Westminster, Tustin, Irvine, Hintington Beach, then the LA FM's are generally not a problem. But once you get into south Orange County (in the hills) of Aliso Laguna Niguel Viejo Margarita, the FM's become problematic. And then for San Clemente and San Juan Capistano you are mostly out of luck unless you are near the coast.
For the two of us with HD in the car in Orange County LA HD goes down to about El Toro Road even though the analog goes further.