The correct answer is volume flexibility.
Volume flexibility refers to the tendency to generate below/above the fixed capability for a product, under the endogenous pricing in a two-product setting. It has been found that the value of volume flexibility is a function of demand correlation amongst the products, a consequence, which cannot be illustrated by classical risk-pooling opinions.
Additionally, the value of product flexibility always reduces in demand correlation, and the value of volume flexibility can decrease or increase in demand correlation on the basis of whether the products are strategic substitutes or complements.