  Separation of variables (SoV) is a special property of integrable models
which ensures that the wavefunction has a very simple factorised form in a
specially designed basis. Even though the factorisation of the wavefunction was
recently established for higher rank models by two of the authors and G. Sizov,
the measure for the scalar product was not known beyond the case of rank one
symmetry. In this paper we show how this measure can be found, bypassing an
explicit SoV construction. A key new observation is that the measure for spin
chains in a highest-weight infinite dimensional representation of sl(N) couples
Q-functions at different nesting levels in a non-symmetric fashion. We also
managed to express a large number of form factors as ratios of determinants in
our new approach. We expect our method to be applicable in a much wider setup
including the problem of computing correlators in integrable CFTs such as the
fishnet theory, N=4 SYM and the ABJM model.
