problem propagate masks

[kino_unico]

Hi, I don't know if this is a problem or if I just don't understand how this should work,
I have this image

and the crystal is configured in all the ways that propagate mask has.
mask never

mask reflect

mask refract

mask always


first I see that the reflect mode, transmits the reflection totally opaque.
secondly, the always mode does not make a correct mix of reflect (which I think should be more transparent) and refract mode, but that is not the case.

what should i do, so that the "mask always" image looks like the image below. (this image i have made in photoshop.

[maru]

I am guessing that you want to replace the background in post and you want to see the reflection of the red box in the glass.
I made a similar scene to yours and tried this, and despite the alpha channel looking "wrong" (black), the reflection is there. This is because alpha is not 100% black there. You can verify that by right-clicking in the VFB and sampling the color. As you can see, it is not 100% black.

Let me know if this helps, and if not, please send me your scene.