Yeah, a more accurate measurement would be "baseline + X" - you don't really need to go above the average household size, but you can fit people in way denser than 25m^2 (270 sq ft) if they share common areas. The average dorm room is 230 sq ft (with a roommate!) but the dorm provides common areas and other amenities.

Another thing to consider when comparing countries is what is considered "living space" and what is not - some areas have large porches that are not considered "living space" even though they serve similar functions to what a living room might in other parts of the world.