Moving a layer behind another one to apply a glow effect I've been creating a spaceship and I am now trying to set up the compositing nodes. For that, I am using pass indexes for materials, so I can change the effects in compositing nodes and i am having 3 different render layers: spaceship, afterburn and one more layer for slipstream.

I've been trying to place spaceship layer in front of afterburn so the glow effect of the afterburn would be exactly behind the spaceship and wouldn' t affect spaceship layer itself.

However, I can' t understand what I am doing wrong. Connecting two layers (spaceship and afterburn with glow effects) into mix shader's image sockets and spaceship's render layer alpha wire into the same mix shader's Fac input nothing happens. The spaceship layer doesn' t get placed in front of afterburn.

Here' s also an image for summarizing my problem. In other words, the glow of the afterburn affects the spaceship:
In render tab, film options just click "transparent" to get alpha