The phase diagrams of four binary systems are presented in which one component is a bi-swallow tailed compound and the second is a nematogenic rod-like compound. In all of the phase diagrams studied an induced smectic A phase occurs. According to X-ray measurements the layer spacingdof the smectic A phase is considerably higher than the average molecular lengthL. Depending on the binary system and the concentrationd/Lratios between 1·17 and 2·13 were found. We propose an interpretation of the results on the basis of a simple packing model.