Sorry I'm so late to this party but I was on vacation
Back in a former profession I had a client who owned the largest independent oil distribution company in Southern California. He told me that the way multi viscosity oils work is with an additive that is heat reactive, expanding or contracting. The wider the viscosity range, the more additive, and thus, the less oil in a given quantity. He said that the additive didn't have the same lubricating qualities as the oil and that you were better off, for Southern California driving, with a narrower viscosity range rather than a wider range oil, because the lubricating qualities would be better. I'm sure he used lots of big words in his explanation but I'm afraid I've forgotten them. He seemed to know his stuff.