This paper details the results of upgrading an effective numerical technique (derived for multiple-scattering simulations in photon correlation/cross-correlation with a plane-wave light source) for the modeling of multiple scattering in a laser beam. The off-axis shape coefficients of an arbitrary beam are computed starting from the set of known beam-shape coefficients for an on-axis location by using the addition theorem for the spherical vector wave-functions of the first kind. The discussed technique is verified by comparison with a localized approximation for a focused Gaussian beam and with Barton＇s spheres-arbitrary beam interaction theory. An additional advantage of the proposed technique (self-testing of the computation accuracy by comparison of the off-axis beam-shape coefficients evaluated from two different on-axis origins) is demonstrated.