In case of goods sold but not delivered for which the insured is responsible and with regard to which under the conditions of sale, the sale contract is by reasons of the perils covered under the Policy, cancelled either wholly or to the extent of the loss or damage, the liability under the policy shall be based on the contract price and for the purpose of average the value of all goods to which the clause would in the event of loss or damage be applicable shall be ascertained on the same basis.