Have you read "The Influence of Frequency, Intensity, Volume and Mode of Strength Training on Whole Muscle Cross-Sectional Area in Humans" by Mathias Wernbom, Jesper Augustsson, and Roland Thome?
Yes. I have read the article. I had mentioned about the article in the comment section of my article.
I think those are pretty reasonable.
We need more quality RCT like these to figure out what's happening. They did a pilot study which showed similar result and same trend was seen with older adults which add credence to their results.
The study basically shows that there is a ceiling effect to protein synthesis and you hit that ceiling by around 10-15 reps. Increasing load further will not increase protein synthesis and may increase protein breakdown.
The authors think that volume might affect the duration of protein synthesis and intensity the peak.