At the moment this works as follows. You select linework and run the selection and it rigidly includes only that linework and completes a polygon boundary excluding anything that is not in the tight shape.
Can there be a different option that would follow the selected linework and then make a tight boundary that includes exerything else.
This may mean some futher editing where the tight boundary strays inside your desired shape, but at least it is following some lines, and may be the option that involves the least amount of editing.
Ok, so First image is the plain file.
Second image is with Tight boundary, created with linework, the strings to the south and East were selected. Note the points and strings not included within the boundary.
Third image is Tight boundary without linework selected, or the with linework box ticked.
An example screenshot would be really helpful. Thank you.