House of representatives is not designed to provide proportional representation based on aggregate % vote country wide. Senate is more aligned that way and it's reflected in the numbers, in AU:

Current US senate (100 seats):

  Republicans: 53 seats (Majority Party)
  Democrats: 45 seats (Minority Party)
  Independents: 2 seats

Current AU senate (76):

  Australian Labor Party: 29
  Coalition: 27
  Australian Greens: 10
  Pauline Hanson's One Nation: 4
  Jacqui Lambie Network: 1
  Australia's Voice: 1
  United Australia Party: 1
  Independents: 3

So Greens are slightly over represented in the AU Senate based on aggregate vote if 12.2% is correct.