Compound setup

hi, in a compound setup where I let the first(bigger) turbo flow free. Will the small turbo have any effect on the boost as the boost from bigger turbo will be inlet to the stock turbo and boost out of stock turbo boost pipe.

With waste gate open all the way stock makes 5 psi. Assuming the cloosed loop when sensing more boost will open waste gate all the way the stock is doing 5 psi. How much will it multiply the boost?