The alpha channel seems fine, as everything else that’s supposed to be transparent comes in that way, its just the plane I’m using as the reflective surface doesn’t. For example, I tried setting the plane to pure black, then set its blend mode to add. In theory, that should make the black effectively transparent against the background. If I put in a background in the motion project, I get the effect I want, but if I take out that background, then import the project as a template into FCP, the black surface just shows up as black, no matter what’s is blend mode is set to. It’s like FCP just ignores it.
What I really need is a way to effectively set the fill color of the plane to transparent, but if I cut the opacity of the plane to try and achieve that, the reflections just disappear along with the color.