5331.6 is not the same as (51.6)(31.6)(31.6), however
The reason we multiply with 1.6 on every dimension is because the ruler we use is 1.6m long. We effectively create a new unit, and have to convert. If a length is 5 person wide, then in reality it’s 5*1.6 = 8 meters long, where 1.6 is the conversion ratio from the unit of ‘person’ to the unit of ‘meter’. And this applies for every individual measurement.
Also, 5331.6 is not the same as (51.6)+(31.6)+(31.6) in the first place