Problem changing face_recognize package parameter

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I follow the procedure in face_recognition wiki page,and successful run the Fserver and Fclient. But It can't recognize my face ,It seem confidence_value set to 0.88 is too high for my camera, so I want to change the parameter. Since I can't see confidence_value parameter using "rosparam list". I want to know how can I change the confidence_value parameter. And I notice that in wiki page, parameter name always will has a prefix ～，but face_recognize parameter do not have one. is this make the different.