Bartosz Milewski on Nostr: Agreed. What I called \(E_i\) is the portion of E allotted to the i'th mass ...

Agreed. What I called \(E_i\) is the portion of E allotted to the i'th mass eigenvalue--your \(|\alpha_i|^2 E_i \). The question is, how \(|\alpha_i|\) are fixed. Does every electron neutrino start with the same mixture, or is it determined by the kinematics?