The recently released IEC Technical Report IEC/TR 61000-3-13 for voltage unbalance allocation requires quantitative measures of the propagation of voltage unbalance from one busbar to other neighbouring busbars of a sub-system in terms of influence coefficienst. However, IEC/TR 61000-3-13 does not prescribe a method for their evaluation. This paper carries out preliminary studies in order to investigate the dependency of these influence coefficients on various load types/bases, and proposes a systematic method for estimating them. Proposed method is applied to a 3-bus MV test system and also to the IEEE 14-bus test system of which the results are verified using unbalanced load flow analysis. This new approach could be considered in future updates of IEC/TR 61000-3-13.