A module, included in an electrophotographic printer, for making toner images by a method in which transfer current for electrostatic transfer of toner images to receiver members is adjusted to compensate for ambient variations of toner charge-to-mass ratio (q/m). A predetermined functional relationship between transfer current and a control voltage parameter is utilized. Magnitudes of the control voltage parameter are derived from voltage measurements relating to creation of toner control patches on a photoconductive image-recording member included in a modular electrophotographic printer. Control voltage magnitude is linearly dependent on q/m. The functional relationship, which is characterized by three experimentally determined parameters, is co-optimized for providing efficient transfer of toner images and for minimizing back-transfer of toner away from a receiver member in a transfer station included in the module.