You may have to spend some time playing with settings and looking at SWFs before you find the right balance between quality and file size. To ease your search, Flix includes a number of preset options. You can edit the existing presets, as well as create new ones.
Preset information is in an XML file.
Flix does not provide any special editor for changing this file. Instead, it brings up the file in the Windows Notepad accessory. A simple XML editor would be useful here, or better yet, a special user interface that could do some error checking. The XML is not extremely complex. However, working in a text editor, it is easy to make a mistake.