Well, that's quite a distance. I can tell you that I have had good reception at Avalon, Two Harbors, Cat Harbor, all on Catalina. I have had drop outs in the middle of San Pedro Channel after about six miles out between Catalina and the main land. I also used to sail to the Channel Islands and had good reception at Smugglers Cove on Santa Cruz, and Anacapa. I think the reception is pretty good between San Diego and LA as I recall except for around San Onofre. Been a while since I have done that trip.
The closer to shore the better of course. I have Verizon, I even made a call from the top of Mt. Whitney once.