High-resolution x-ray diffraction studies have been performed on the polar liquid-crystal binary mixture of octyl- and decyl-oxyphenyl nitrobenxoyloxy benzoate (47.4 mole% DB8ONO2 + 52.6% DB10ONO2). At temperatures below 127 °C this mixture exhibits the phase sequence (with decreasing temperature) smectic-Ad—reentrant nematic Nd—reentrant nematic N1—smectic-A1—tilted smectic antiphase smectic- C̃ -smectic-A2—smectic-C2. The development of lateral fluid antiphase fluctuations from the partial bilayer fluctuations in the smectic-A1 phase have been probed and analyzed as well as the transition from the tilted smectic antiphase to the tilted bilayer smectic-C2 phase that is accompanied by the occurrence of an intermediate smectic-A2 phase.