Monte Carlo simulations of charging and profile evolution during plasma etching reveal that the substrate can mediate current imbalance across the wafer. This function couples patterned areas, where the electron shading effect dominates, to substrate areas directly exposed to the plasma. When a net positive current flows through the pattern features to the substrate, increasing the exposed area decreases the substrate potential, thereby causing notching at the connected feature sidewalls to worsen, in agreement with experimental observations.