Does the .mogrt have any other controls, such as, to make the background's Opacity to 0 or to change its color? It really doesn't appear so. We can't see the entire panel, so we'd need another screen shot to tell. You can also tell us the name of the .mogrt so we can check it out.
If you have no other controls, I would make the graphic full screen, then in the Effect Controls panel, under Opacity, explore some of the blending modes like Screen, Add, Overlay, etc. See if you can find a nice way to knock out the black that way. It's certainly the most elegant option.