It really depends on what part of Southern CA you in. My iPhone Xs Max and Note 9 show about the same number of bars. I am in Monterey Park, CA 91754 which has poor coverage with Verizon / AT&T mostly 1 bar unless you are close to East Los Angeles College where you will have full bars of service. T-Mobile & Sprint work much better here mostly full bars all over town due to denser network. Coverage with Verizon is hit or miss in the surrounding areas East Los Angeles, Alhambra, San Marino, South Pasadena usually 1-2 bars. Data can be extremely slow & good thing voice calls seem to work fine due to VOLTE. However T-Mobile practically has full signals in these same areas. Verizon gave me LTE Network Extender so I have full coverage -68 db in my home Band 13. Verizon does get better in La Puente / West Covina with full signal. I am guessing because the landline carrier in the area is Verizon / Frontier. I am using dual sims Phone Xs Max with Verizon & T-Mobile. I use AT&T for unlimited data on my iPad.