I don’t have access to my testing machine for a couple of days so can’t really try to create a test case. But if you are replacing the left or right widget area using the per page option it should work. Be sure you also specify the two columns layout for that page.
1- @weaver, I just tested it, and it appears there is a bug.
If you use the sidebar layout Double col right (bottom or top) when you replace the Lower/left sidebar area it ends up full width above the right column, and if you replace the Upper / Right sidebar widget area, it ends up full width below the left one.
2- It looks like you found it as your two columns are different width. The setting is in Main options > Layout > Sidebar Wrapper Properties > Split Sidebra options
As this is Weaver II, it is unlikely that this bug will be fixed anytime soon. For one thing, in all the time that Weaver II has been out, this is the first time that anyone that has noticed this issue. It just doesn’t currently warrant the costly effort required to fix.