Info: Calif. Vehicle code 5201. License plates shall at all times be securely fastened to the vehicle for which they are issued so as to prevent the plates from swinging, shall be mounted in a position so as to be clearly visible, and shall be maintained in a condition so as to be clearly legible. The rear license plate shall be mounted not less than 12 inches nor more than 60 inches from the ground, and the front license plate shall be mounted not more than 60 inches from the ground. No reference as to minimum height or where, center or side.
Auto or manual holders from under spoiler look to be around 9 inches to bottom of plate. Mounting in loxer grill is at 12 inches, stock postion seems to be around 16.