A method for etching a stack with at least one silicon germanium layer over a substrate in a processing chamber is provided. The dispenser also includes at least a removable orifice plate for controlling the movement of sheet material from the housing through the exit port. Such optimization can be achieved using reliabilities, preferences and policies concerning handling the attempted contact based on a deterministic specification or through inferring reliability, context, content and task under uncertainty by employing decision-theoretic inferences.