These numbers were made by Peugeot in 2003 models during composing. You can use 526 liters capacity of trunk in Peugeot 406. You also may put the back seat of 406 down to receive more space than 390 liters. The trunk shape of Peugeot’s design proves to be useful. You may always put small shopping things in 406 trunk.
Overloading Peugeot 406 might be a great problem in future. Check also if your luggage in 2001 Peugeot isn’t heavier than needed. The number of 430 liters cargo space is provided by Peugeot and is appropriate for vehicle.