The existence of a third phase interphase in polymer composites is well known, and there have been many attempts to characterise the mechanical properties of this region at the nanoscale. Despite the increasing resolution of nano-indentation and atomic force microscopy techniques, it is not always possible to measure thin interphases when the dimensions are similar to those of the indenter-surface contact area. The use of indentation for mechanical characterisation continues to be explored for multi-phase systems, and there is need for a method to evaluate quickly whether a given indentation is influenced by neighbouring material phases. The results presented in this paper demonstrate, both experimentally and through finite element analysis, a method of quickly identifying indentations that are restricted by the reinforcement.