I think if you know CA, then you're less likely to be critical of the ratio. I can say that I have no plans of shopping or going to OC beaches any time soon, something of which I used to do weekly.
Regarding Disneyland: Our pass holders come from all over Socal as its just an hour drive from virtually the entire southland region (without the dreaded traffic of course). I mentioned here before that you may as well consider LA and OC one in the same as its easy to populate both in the same day. The problem with that is there are so many different characters in CA, and these characters often neighbor each other. So you have super anti mask OC and super pro mask LA mixing with each other 24/7. These are not small towns in the midwest, these are two large economic cities with lots and lots of people, making spread easier.
I think the ratio for yellow is appropriate. It helps ensure that the numbers are low enough to create a safer environment for this type of large attraction. San Bernardino for example, just went back into the purple tier. There are thousands of pass holders in San Bernardino. A lot of CMs also work at Universal, which is cross town in Hollywood. It needs to be consistent so that once a region is yellow, the numbers are low enough so its easy to gauge and control growth.
Regarding the percentage of people allowed in, Id say if we are in yellow, a capacity of 25% is low. By that point we should feel stable enough that say you could at least push it to 35% to start out and grow from there.