Hi
Vignette only works for the full 16:9 frame and is not effected by what the frame contains. 
It's a bit limited as it is.
If you pull the width value to the top (0.5) and the strength value to the top (3.0) it's the closest you will get for your particular AR, but there wouldn't be any room for animating it---even if you could.
It would be nice to be able to add a vignette that could be reduced to just the centre of the frame.
However it is possible.......sort of....
Place your main clip on track 1
Add a black blank frame to the overlay track directly above this and then add a Round transition to the blank frame.
Move the red cursor along the sequence into the orange bar and stop when the the "vignette" in the preview appears of the size required for the height of your particular image size.
Left click the main clip and slide it along to the right of the cursor line...don't move the cursor line.
Now take a snapshot at the cursor position.
Delete the blank frame from the overlay track and replace it with the snapshot which should be a circular vignette of the correct height.
Replace you main clip beneath this.
Play the sequence, you should have a circular vignette.
You can make it oval by increasing the SCALE width effect.
e.g.
Note that TEST2, the main clip/image on track 1 has an AR the same as your own with the bars at the top and bottom.
Nat
