Recently we have exploited non-equilibrium effects in the preparation of super-efficient polyelectrolyte/surfactant films at the air/water interface spread from the dissociation of liquid crystalline aggregates as they come into contact with pure water. The ability to form extended reservoir structures in these films upon repeated spreading or surface area compression is dependent on the charge/structure of the aggregates used in their preparation. Such tuneable formation of reservoirs in a fluid film has not be demonstrated before, but the structures of the films remain a mystery. Here we propose a short set of measurements using the INTER reflectometer for the first time to gain valuable insight into missing structural aspects of the reservoirs. The focus is the versatile system PEI/SDS as a function of the charge of the aggregates used and the charge density of the polyelectrolyte.