From what I have seen/heard in the valley of silicon, the really insane high schools (Gunn, Paly, Saratoga, Monta Vista, Lynbrook, Mission San Jose), the majority of the kids in BC are 11th grade Asian kids. Of course the Asian category is nebulous since you have the East Asian/South Asian kids (Chinese, Korean, Indian) who are the high achievers and Southeast Asian kids who don’t have the resources and don’t end up in the AP classes.
Son’s BC class of 30 kids had 5 seniors and they happened to be non-Asian. The only senior who happened to be Chinese decided to drop down to AB. Didn’t affect him that much since he was accepted to WashU for BME.