David... you got this one inversed. South OC's population possesses the much greater population:
Mission Viejo 95,638
Lake Forest 84,666
Laguna Niguel 65,048
Aliso Viejo 50,385
San Juan Capistrano 35,976
Laguna Hills 31,613
Laguna Beach 22,991
Lancaster 157,697
Palmdale 153,240
Already, from just the 7 cities I itemized South OC has L/P beat 385K to 311K; and that's before even factoring in additional South OC places like Ladera Ranch, RSM, Coto, San Clemente, etc.
Bottom line, South OC is an important population geography for radio signals to attempt to cover within their 60 dBu contour if they can.