The study reported in this paper addresses an aspect of the modelling of particle stratification as it applies to the processing of minerals. It focuses on the phenomenological model developed by King and the extent to which the single parameter in that model, i.e. the stratification index, is dependent on the size of particles in the stratifying system. Based on a careful experimental investigation in a batch jig, the study found that, contrary to expectation and current theory, the size dependence of the index is weak or absent over the range of conditions investigated. The implications of the findings for both theory and modelling practice and for Rao's proposed modification of King's model are discussed. The study also presents a number of findings related to experimental procedures for obtaining precise measurements of parameters in stratification models.