An electro-processing apparatus has a contact ring including a seal which is able to compensate for electric field distortions created by a notch (or other irregularity) on the wafer or work piece. The shape of the contact ring at the notch is changed, to reduce current crowding at the notch. The change in shape changes the resistance of the current path between a thief electrode and the wafer edge to increase thief electrode current drawn from the region of the notch. As a result, the wafer is plated with a film having more uniform thickness.