Ion and electron properties are measured in a helicon plasma source to characterize the plume when the magnetic nozzle throat is axially shifted with respect to the antenna center and to study the electron cooling rate along the magnetic streamlines as the magnetic nozzle divergence is varied. Larger ion currents and increased plasma confinement are achieved when the throat of the magnetic nozzle is located downstream the antenna center, at a distance that equals or exceeds two times the antenna length. Furthermore, the electrons polytropic index shows dissimilar values along distinct streamlines. It is suggested that ionization phenomena and reduced cross-field transport are responsible for departure from adiabatic conditions.