Idk man, to me it just looks like shading, like he did with hakuba:
For example, 1018 shows the difference quite well with Jinbe and WsW's haki:
In greyscale, unfortunately its just not that easy discern. But also thinking about it logically, CoA should increase hardness, not pure strength. I wouldn't expect Robin to even need to coat her whole body to clutch Black Maria. It shouldn't change her strength to clutch anyway.
You can also see what I mean here when you look at Robin herself. Half her face isn't even shaded when in that form :
There is a "shininess" to CoA, this shading and Hakuba lack it imo.