The connection of the FB multiplicity correlation coefficient b in windows separated in azimuth and rapidity with the two-particle correlation function C 2 is traced. Basing on this connection the general features of the dependence of the correlation coefficient b on the acceptances of the observation windows and the rapidity gap between them are found a model independent way. It is demonstrated that the traditionally defined FB correlation coefficient b has the strong nonlinear dependence on

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... e acceptance of windows, going to zero with the acceptance. In this connection the suitable observables for the future FB correlation studies are proposed. It is shown a model independent way that the measurements of the FB correlations between multiplicities in two small windows separated in rapidity and azimuth enable to find the two-particle correlation function C 2 even when the particle distribution in rapidity is not flat, as in pA scattering, i.e. when the traditional di-hadron correlation analysis is not applicable.