My brother is a highway patrol and takes radar all day. He laughs at cops that write tickets for 5PM over the limit. He sets his radar gun at 20+ over the limit for the same exact reason that you describe. Because he wants to write a ticket and not have to get into a conversation with the driver. He figures if you are going more than 20 over then he shouldn't have to hear "I can't believe you wrote me a ticket for only going XXX over the limit". He says even if he only gets the 20+ over the limit there are plenty of tickets to write... he doesn't have to waste his time on guys like you only doing 9 over.