Presented herein are trans-modiolar stimulation techniques in which stimulation current is sourced by at least one intra-cochlear stimulating contact and is sunk at a group of other intra-cochlear stimulating contacts. The coupler is placed on the substrate, wherein the coupler is vertically aligned to the OE device. The method also includes receiving physical count data associated with each of the part numbers in the first group and the randomly selected part numbers from the second group.