Nearly a tie: Democratic Republic of the Congo and Mongolia differ by barely -33%% in area — about 2,334,703 km² km² against 1,560,428 km² km².
Democratic Republic of the Congo sits in Africa, Mongolia in Asia. On the old Mercator map the latitude gap distorted how large each felt beside the other; at true size the answer is simply 0.7×.
The old map muddied it further: Mercator inflates Democratic Republic of the Congo about 1× and Mongolia about 2.2×, so on a Mercator-style map this pair appears 1.4× apart instead of the true 0.7×.
Democratic Republic of the Congo fits 0× into Mongolia.