The LMS primaries has the biggest impact in color. The LMS compression has impact as well, but that’s a technical necessity, as explained in the beginning of this thread.
The custom eccentricity factor has only a small impact. The eccentricity factor is actually part of the chroma compression gamut (not related to gamut mapping limiting gamut), and that has bigger impact. It is what was introduced v032 with the new chroma compression algorithm. It effectively limits how much chroma compression compresses, with the intention of protecting purer colors from being over compressed. This is done in the name of getting tighter inverse, with the goal of being able to invert Rec.709 to AP1.
I have no doubt the forward direction could be made better if there was no need to invert. And it could be made better if we didn’t have the need to invert to AP1. IMHO, AP1 inversion is a tough requirement because the source camera material, even in best cases, is going to be within AP0, and in practice often outside AP0.
But the question I still have is, why is the blue so dark in this model? ZCAM didn’t have the blue this dark. Not in the higher exposure levels, and not in the lower either. I don’t think it’s just the LMS primaries. It may be the lightness metric, which is why I started playing with the achromatic response. But I’m still none the wiser.
The best blue I’ve seen with this model is the prototype version from the top of this thread with an LMT that makes the blue brighter. Not only will it retain saturation at higher exposure levels longer, but by also making it brighter it makes all these challenging images look better (and match HDR better).