Experimental and theoretical results are compared to explain the dielectric properties in the S*(C alpha) phase of two homologous of the nFF series. Using the clock model and calculations developed by N. Vaupotic and al., the temperature evolutions of the Goldstone and soft modes in the S*(C alpha) phase are studied. Two different behaviors are evidenced depending on the azimuthal angle difference a between two adjacent layers: when cc is limited, the Goldstone mode is detected in all the S*(C alpha) phase; for higher values of alpha, the soft mode is predominant near the S-A-S*(C alpha) phase transition and the Goldstone mode is observed only at lower temperature. A good agreement is obtained with previous experimental results in considering the influence of the azimuthal angle alpha and its temperature evolution. These predictions are confirmed with optical period measurements performed on the same compounds.