High-resolution x-ray diffraction studies of a binary mixture of the n = 8 and n = 10 homologs of alkoxyphenyl nitrobenzoyloxy benzoate DBnONO2 (52.6 mole % DB10ONO2) have been performed at the onset of the tilted smectic antiphase (Sm-C) upon cooling from the smectic-A(1) phase. Fluctuations of the two competing smectic orders are found to be related to monolayer and partial bilayer ordering. With decreasing temperature, the period of the antiphase in-plane modulation increases while the smectic layer normal tilts at an angle of +/-7 degrees with respect to the director. This tilt partially recovers upon the transition to the smectic-A(2) phase.