
I've made this mask:

and I can use it in Vegas video to create the effect I want. However, when I drop that bitmap into the Resolume mask folder, and apply it as the layer effect, it is not quite the same. The white parts of the image never become 100% opaque while the dark parts are 100% transparent.
How can I do this?
I would like most of the inset picture to be opaque, while the background fades in at the bottom.