If he’s afraid of “too small,” you could start by looking at the Claremont Colleges. Even though each college is small, it’s a very close consortium with all of the campuses connected and walkable, joint EC’s and athletic teams, and cross-registration that is seamless and widely utilized. In many ways it’s like a mid-sized university, with about 7000 undergrads. He could major in physics at any of them (except Scripps, which doesn’t admit men), although Mudd would probably be the best fit.