The figure was formed by Honda during designing the 2015 year models. It’s convenient to put small luggage in Insight cargo space. You may find over 461 liters of space in Insight having put down the back seat. The trunk shape of Honda’s design proves to be useful. In Honda Insight you get 461 liters of free space in the trunk.
But don’t forget about weight rules of 2000 Honda. The number of 461 liters cargo space is provided by Honda and is appropriate for vehicle. It’s easy to overload Honda Insight but try to avoid this.