Select the variation of tie for which you would like to adjust the placement settings. There are a number of selections in the drop-down menu. There are separate settings for ties that are inside chords, and ties that are the outermost ties on chords (note-side and stem-side). Each of these have separate settings for ties over notes and ties under notes.
When you are adjusting these settings remember that the notes tied together may not use the same choice from the drop-down menu. For example, ties with mixed stems may use different outer placement settings. To have Outer placement settings take effect, the Use Outer Placement check box must be selected.