Sigma and Products

Hi Sorry ... nothing deep or fundamental here. Here is a simple question which someone may know the answer to. Lets say we have a fibration p:E -> B with left adjoints Sigma_f for every reindexing functor f^*. Lets say further that E has products and p preserves them. Are there simple conditions under which we have Sigma_{f \times g} (P \times Q) iso (Sigma_f P) \times (Sigma_g Q) All the best Neil [For admin and other information see: http://www.mta.ca/~cat-dist/ ]