You know how on Star Trek Kirk always needs something fixed within 30 minutes but Scotty always need an hour to fix it. In the TNG episode "Relics", Scotty admits that he always asks for more time than he needs to fix something so that he gets a reputation as a miracle worker.
I think Graham Richards had a similiar strategy when he asked for a 30% raise. He knew City Council wasn't going to give him all the money that he asked for. If he asked for 10% they would have given him 8%.
This is also why FWCS Superintendent Wendy Robinson is asking for $995 million dollars, so that people feel more comfortable forking over $300 million.
Whether you're selling a car, asking for a raise or budget increase, or fixing a warp coil, asking for more than you need or deserve is a common tactic.