I think you want to set Diagram.PrintManager.PageOptions to include the “Full” page flag.
Yes, depending on how large the objects are that you want to render outside of the printed diagram area, the Margin might need to be a Thickness of the corresponding size, at least in that direction.
Setting the Page Options is not solving the problem. Actually we have implemented Print Preview in which we are reducing the printable area of the diagram to half of the papersize as we need the same for export to AutoCAD.
I’m not understanding what you are doing. Are you unable to set PrintManager.Scale to a value that you calculate?