A method of operating an implantable neuromodulator coupled to an electrode array implanted adjacent tissue of a patient includes conveying electrical modulation energy to the tissue per a series of modulation parameter sets, thereby displacing the locus of the resulting electrical field laterally relative to the tissue, associating a plurality of different loci with the modulation parameter sets, causing the patient to perceive paresthesia, identifying a modulation parameter set as creating an electrical field having a locus disposed on a physiological midline of the patient based on the perceived paresthesia, deriving another modulation parameter set from the identified modulation parameter set, conveying electrical modulation energy to the patient per the other modulation parameter set, thereby creating an electrical field having a locus relative to the tissue that is the same as the locus of the electrical field associated with the identified modulation parameter set, without causing paresthesia.