Invoice design - position address to show through envelope window

Hello, I want the address on my invoice to be in the correct position to show up in the A5 window envelope window. Can someone please tell us how to position the address to enable this. At the moment we can change the page borders only and not indentation for specific parts of the invoice. Moreover the borders seem to only apply to online views and do not change the borders on the pdf. Why is that? Please think about how we use the pdfs, it is usually to post out to people. Thanks.