^^ to add
"Geoffrey Zatkin answered a question in 1999 where he claimed that charisma had a role in charm durations. He was also either wrong or charm changed before PoP went Live...As a developer myself I can attest that it's easy to get stuff wrong when taking a cursory look at code, so disputing developer claims isn't as presumptuous as it seems."
https://youtu.be/gqW42BFqVjo at 23:10 Geoffrey Zatkin talks about designing enchanters... 30:10 when he mentions charm.
Just saying, I don't think he was "taking a cursory look at code" when he said CHA effects charm duration considered he designed them.