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How to recreate an "iClonic AO channel"?

I am looking for thoughts on mimicking the operative performance of an iClone material channel, in UE4.
Specifically, the channel is iClone’s ambient occlusion, “AO”

As background, in its material settings, iClone’s AO channel acts as a “fake AO”, in that it is ‘paintable’ and ‘forced’ shadowing for a texture. In that, the lighting of a scene is not generating this AO, rather the texture is. So you can ‘fake’ an AO on an object.

ie -
(1) you have a flat 1-sided plane mesh
(2) you have Texture A, a red 512x512 square in the Albedo/diffuse slot
(3) you have Texture B, a white 512x512 square with a black “X” in the center, extending to both ends, in the AO slot

When rendered, the flat plane will be red, with a ‘shadow’ X on it, and this shadow strength can be accented via an AO-slider from 0 to 100 (min-max, respectively). iClone ignores the white, and only prints the black from the AO slot, onto a material

But, in trying to create such a thing in UE4, the white background of the “AO-X” texture will brighten the red to a pink using either LINEAR INTERPOLATE or MULTIPLY-ADD node (Lerp or Multiply), as it computes the white as well.

(Naturally my first thought was just plug in “AO-X” texture to UE4’s AO slot, but it appears non-operative.)

Is there a way of linking the nodes together to just allow the black X to be shadowed on the red base color, without the white of the “AO-X” map being computed as well? When I try to mask out the white I wind up masking out the whole thing, the black goes away too. I am trying different versions of linkages and alpha maps, but none give me the desired end.

UE4’s emission texture omits the black and prints the white, I am looking for the reversity of this, ignore the white and print the black.

Thanks for any thoughts or ideas!