High resolution calorimetry studies at the smectic-A to nematic phase transition confined to the random interconnected voids of Millipore filters were performed. Measurements took place with pure 9CB and (9 + 10)CB mixtures, for bulk and in 0.05 mu m void size Millipore samples. This work focuses on the competition between the confinement which affects the bulk-like critical behavior by weakening the coupling between the nematic and smectic order parameters, and the increased coupling that results from the addition of a smectic liquid crystal component.