Hi gvzmedia,
I have no scene file, so I assume it is the rendersetting, and not the AO shader.
Ambient Occlusion is not interested in any material. It is a pure geometrical result, based on the edge and the neighbor’s angle to each other.
This kind of Geo-AO was developed in a time were animated GI was prohibitive in render time. It does not even have a clue if there is a light in that corner; it will deliver a dark result even with the brightest light in that corner.
AO is typically part of a well set GI solution (here as “natural” exclusion of the light), to have it on top of that solution is not really a correct procedure, if you use GI at all.
There are options to get it working, even it is not based on any light, but it needs to be baked and placed into the Diffusion channel (while the checkbox is set for affecting Illumination).
Second option: rendered out as a pass and integrated into the multi-pass calculations. There I think the cheapest way to do it is via multiplication on top of everything, or more appropriately used as a mask in an adjustment layer, and with that used to adjust the brightness as well as the saturation of that area. Less light, less saturations.
As I mentioned, I have no file here, and as I write in a forum, I suggest the basics of comping here as well, since artists reading along have a wide variety of backgrounds.
Geometric based AO is often used on top of the existing GI-based AO; if so, I believe that no one really cares if it is just set to darken or plainly multiply, perhaps with a little bit of adjustment of the opacity in the comp. I assume that Multi-pass is done in float and linear. If done with Gamma, please note that the image-based (v. data) use needs then a profile included, and the mask use should be read as values, but based on linear results, of course.
My best wishes
https://help.maxon.net/us/index.html#VPAMBIENTOCCLUSION-ID_VIDEOPOSTPROPERTIES
