The electrodeposition of nickel into an angular trench in the presence of coumarin, a widely used inhibitor, is simulated using boundary layer approximations representative of flow parallel and transverse to the groove. Based on the diffusion‐adsorption mechanism of leveling action, the dependence of the developing contours on variations in the Langmuir coefficient and inhibitor/metal‐ion flux ratio are investigated. Leveling efficiency is shown to be highest for thin, planar boundary layers, and lowest for contour following boundary layers. The model successfully predicts the leveling‐off of the inhibitor effect with increasing inhibitor vs. metal‐ion flux, and that there is an optimal mass transfer boundary layer thickness, or flux of additive which results in superior leveling performance. Satisfactory agreement is found between the predicted contours, obtained by solving the model equations using the boundary element method, and the experimental leveling efficiencies determined by previous investigators.