blending transparency on multipass render

I have a multipass render setup for two passes. The first pass I want this texture to be drawn with 20% transparency. The second pass I want to be drawn with 80% transparency. What I get is the top layer blended, like a subtractive blend, into the lower layer witch is at full 1.0 alpha. My guess is that I am setting up the belending wrong but I don’t know what else to try.

I want the second pass, top layer, to only have transparency added to it and not added or subtracted to the lower layer. I mean I don’t want the texture to change color values, but have the appearence of added alpha to the entire texture, even if there is an alpha included in the texture.

Any ideas?