KDE Tip: If the Display Settings snapping is preventing you from getting the alignment you want (eg. top-aligned 1280x1024,1920x1080,1280x1024), try changing (but not applying) resolutions, then snapping, then changing them back.
(eg. To work around the forced centerline snapping, I changed the 1920x1080 to 1280x1024, snapped them together as a uniform row of 1280x1024, changed it back, and then hit apply).