At Berkeley I know of a transfer who got put in a residence hall with freshmen - and he had not requested it and hated it. I was put in a suite with one sophomore and two freshmen. And the building was freshman-sophomore-intensive. I HATED IT. Where you ultimately get placed has to do with space. You could indeed end up with freshmen, especially at the UCs where space is tight. They’re forced to cherry-pick the students who get funneled into the less desirable spots. Quite a few transfers at Berkeley ended up mixed in with freshmen. I doubt you will like it. Trust me.
They probably have more room at Davis but if you want a residence hall I’m sure you can switch with someone during the open period after the term starts.