G'Mic HaldClut Before/After colors don't match?

Software G'MIC
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Goal: Use colors from an in-camera Sony “Picture Profile” to generate a CLUT.

Process: Shoot RAW+jpg. jpg has an in-camera LUT applied. Using RT “linear” standard Color Management (ie: Tone Curve disabled), generate a second jpg. In the Gimp run G’Mic Before/After to generate a new HaldClut.

Problem: G’Mic Before/After generated HaldClut applied to the RT processed jpg doesn’t quite match the input file tones nor contrast (though I can kind-of get there thru further processing).

I’ve read through some of the discussions here and, if I read correctly, there seems to be the potential for variation.

Question: Is there a process or base setup where I might more accurately match colors and contrast?

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Hey, I added some tags and am posting to give your query more prominence. Please provide sample images.

Curious: Is there are a reason for you to go this route rather than Auto-Matched Curve[1]?

[1] Speaking of which, why does this reference page not exist anymore on RawPedia: Auto-Matched Curve? Quite a few pages reference it, including Getting Started.

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Thank you @afre for adding the tags.

Here’s a link to the comparison I’m working from - Gimp G'Mic Before/After Comparison | Christopher Perez | Flickr

I’m not sure what Auto-Matched Curve can do for me in this instance, but am very happy to learn.

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@afre - Thank you for your question about my not using RT’s “Auto Matched Curve.” It solved the problem. To prove that, I’ve updated the samples I posted on Flickr - Gimp G'Mic Before/After Comparison | I used this to illustra… | Flickr