When adding a new empty panel, it's placed at top by default, but it should be placed to bottom, when it's possible. Also when adding a new "Default Panel" to second screen without any panel and you already have one on your first screen, then it's also placed to top instead of bottom. This is just a simple fix, which changes order of checking free edges for empty panels and adds a check for screenId when executing a script for default panel layout. I'm not much sure with the javascript part, but it works.