Ferroelectric liquid crystal devices are primarily of interest owing to their truly bi-stable operation and fast switching times. At present our understanding of the switching processes in ferroelectric liquid crystal cells is incomplete. In order to develop a more complete understanding it is necessary to have a detailed knowledge of the optical tensor configuration adopted by liquid crystalline materials in cells. In this paper we present results of a half-leaky guided mode study of voltage induced elastic deformations of the director profile in a cell containing a homogeneously aligned 40% chiral mixture of the ferroelectric liquid crystal SCE8. The experimentally deduced changes in the director structure are highly accurate and may be used to test theoretical models of surface stabilised ferroelectric liquid crystal devices.