Ferroelectric liquid crystal mixtures with the various values of spontaneous polarizations were prepared, and the substrates were coated with different thicknesses of aligning agent. The frequency dependence of the electrooptic response of these materials in cells with various thickness of alignment layers has been measured. The coercive voltage as well as the contrast ratios are calculated. Out, results support the "electrostatic model", according to which both the value of spontaneous polarization and the thickness of the alignment layer play important roles in the V-shaped switching.