Florida’s largest property insurance company on Wednesday proposed an average increase of nearly 430 percent for optional sinkhole coverage in response to soaring claims and 8.8 percent for all other perils, including hurricanes, fire and theft, all effective in 2012. The board of state-backed Citizens Property Insurance Corp. voted 4-0 to ask for approval for the higher rates from the state’s Office of Insurance Regulation. Two members abstained because they are Citizens agents.