Actually they could make what i would call the "size" of the tank much bigger and change it internally to only hold 200 litres if they wanted to add weight to the back of the car. However in this case the size of the clubhead itself is limited to 460cc's wich is what it displaces not what it can hold. Size is an
extremely
subjective term, however, and most certainly does not equal volume only or there would be no need for the word volume. For instance the "size" of a river or lake is generally measured by how long and wide it is but not by it's volume of water it holds.