We report the results of a theoretical study of the complex phenomena relating to contact angle changes for hexadecane droplets on a gold surface in aqueous ionic surfactant solutions. This approach integrates changes in the nature of the solid absorbed surfactant phase through use of the quasi-chemical approximation. This improvement is accomplished with minimal additional model complexity and provides evidence for changes in adsorbate structure as aqueous surfactant concentration is increased. The theoretical predictions are tested using previously published data regarding the contact angle of hexadecane on gold in sodium dodecyl sulfate and cetyl-trimethylammonium bromide solutions.