Burning rate variations of different matrix formulations as a function of pressure and binder lamina thickness of sandwiches are presented in this paper. These matrices based on ammonium perchlorate (AP) and hydroxyl-terminated polybutadiene (HTPB) cured by isophorone di-isocyanate (IPDI) exhibits mid-pressure extinction in certain pressure ranges for some fine AP/binder ratios. Pure AP self-deflagration rates and pure binder sandwiches are also examined for the same pressure range. Fine AP filled binder (matrix) sandwiches for high fine AP loading show plateau burn rate trend in the 20-80 bar pressure range. The results obtained for burn rate of matrix sandwiches with binder lamina thickness shows an optimum thickness of maximum burning rate only at higher pressures and not significant at lower pressures for sandwiches with less fine AP loading in the binder. The optimum thickness for sandwiches shift towards higher thickness as pressure is increased in case of matrix sandwiches and shift towards lower thickness for pure binder sandwiches.