Applying effect to title background mask?

I am trying to create a title for FCPX 10.1.4 with Motion 5 (the latest version).

I want it to be a lower third with a blurred background so that the footage is still identifiable but doesn't distract from the text. Imagine this like a normal lower third with a rectangular background the text is projected on, just that the background is not a solid color but the blurry image of what's underneath. I used a Gaussian blur effect for the footage and a mask that fades in and out, unfortunately this leaves me with a black background in FCPX and the only thing visible is a small portion of the background, blurred and beneath the title. I would like the black background to be the normal background and not the black color. None of the compositing settings seem to work. I tried adding a drop zone but unfortunately that adds a second source and it's very complicated to pick exactly the footage that lies underneath the title when it appears. The background color in Project Settings has no effect on the title so when I set that to white the outcome is still a black screen.