Concentrated micellar solutions of the binary system sodium lauryl sulfate-water and the ternary system sodium lauryl sulfate-water-decanol have been studied by X-ray diffraction in the vicinity of the isotropic (I)-type I hexagonal (H-alpha) liquid-crystal phase transitions. Results show how decanol affects the I --> H-alpha phase transition. In the binary system there is a close packing of micelles in a local hexagonal order in the I phase, and the H-alpha phase has a behavior typical of finite/hard objects. In contrast, in the ternary system the close packing is relaxed through a micellar growth, and the H-alpha phase has a behavior typical of infinite/flexible objects. An intriguing phase sequence H-alpha-nematic cylindrical (N-c) with an increase in the decanol content is also investigated, and it is attributed to a combined effect of micellar growth and change in rigidity with decanol addition.