OK I will try again
I just prepared 2 short movies.
One with 2 series, where one of the series is not visible. This invisible series is "AreaRange" type. In this movie you can see that the toolpit it's always close to the mouse pointer. I just drag the cursor always in the same vertical position and the tooltip doesn't give any jump in the position. The tooltip is always with the bottom part on top of the cursor and the horizontal alignment to the center.
The second movie is with 3 series where this "AreaRange" serie it's visible now. Doing the same movement like in the previous movie the tooltip jump positions between series. The tooltip seems to have different alignment because of "AreaRange" serie. On A bigger chart this behaviour is more visible. When the cursor line crosses a serie "AreaRange" the tooltip alignment changes vertically (middle alignment instead of bottom like in the other series) and horizontally (right alignment instead of center like in the other series).
I tried already using the position function but I prefer to keep the tooltip close to the cursor.