Madagascar dwarfs Oceania: about 594,622 km² km² against 8,600,000 km² km². At true size Madagascar is about 14.5× larger — the whole of Oceania fits into Madagascar roughly 14 times.
The old Mercator map treated both about equally (1.1× vs 1× inflation), so at least their relative sizes were preserved — even if both were drawn at the wrong absolute scale.
Madagascar fits 14× into Oceania.