The Dropzone as it is won't allow you to do anything but one of three 'Fits'. But you can modify it to do any form of fit you want.
Right-click on the DZ and Group it. Change the group to 2D.
In that new group, duplicate the DZ and name the duplicate 'Mask'
Select the original DZ again and apply an Image Mask (it's not a Behavior. It's in one of the main drop-down menus).
Drag the layer now named "Mask" onto the Image Mask layer.
I'm doing this from memory and if I have it right, you can now apply your 16x9 image onto the DZ and size it the way you like.