Automated painting of a shoe sole portion is enhanced by use of a mask cover (420) and an air knife (422) with a paint assembly (410). The mask cover is positioned in front of a paint-emitting portion (416) of a spray nozzle (414) and is adapted to obstruct at least a portion of the paint intended to be emitted by the spray nozzle. The air knife is coupled to the mask cover and is adapted to emit a laminar fluid flow over the mask cover. The laminar fluid flow helps to limit unwanted diffusion of the paint as it passes along its intended spray path.