The percentage is based on the wrong item. It needs to be based on the universe, not the person.

For instance, say the universe is 100,000 sq feet (obviously not, but just easier math). The difference between a 5 foot person's volume and a 6 foot person's volume is, let's say, 1 sq foot nice and tidy.

The percentage difference is not the difference between 5 sq feet and 6 sq feet, it's the difference of 1 sq foot our of 100,000. So the universe (in this argument using fictitious numbers) would be 0.001% smaller to the 6 foot person.