https://www.ncbi.nlm.nih.gov/pmc/ar...3-life-04-00295

You have a point that they might not be pushing the protein envelope to the point of diminished returns. Here they actually worry that increasing protein past a point will result in increased bone loss. Mmph. A bit late to dig into whether they have some special low gravity related reason for this, or are just playing that old saw about acid/base balance versus bone mass...