Others will add to the list, but I’d look at Case, WPI, RPI and Lehigh. They are small, but have good facilities and tend to offer good merit aid.
There are a few extra things to note about CA publics.
First, they’re not using standard tests, so the great SAT won’t help.
Second, for all but UCB and UCLA, both of which are holistic, EC quality isn’t that important. At Cal Poly for example Tenderfoot and Eagle are the same. It’s all about hours devoted and leadership positions, no matter how mundane.
Lastly, Cal Poly is indeed bigger than he might want, but he should know it comes with some small school advantages. Classes are small. Calc is capped at 32. Physics 40something. The largest lecture hall in the whole CENG seats 130. Lectures, labs and discussions are nearly all taught by instructors with terminal degrees. They don’t offer PhDs, so there’s no pool for TAs.
Good luck to your student!