That's a good point, I was grouping IRV and PR-STV when proportional representation isn't a guaranteed component of a ranked-choice system (though many of the dem implemented RCV systems do use it for things like county board or city council seats). Australia's House does use IRV and is at 12% (or 15% if you subtract two vacancies from the major parties).

Also to note, there's nothing technically stopping the US House from moving to proportional representation along with ranked-choice and dems have proposed it recently: https://en.wikipedia.org/wiki/Fair_Representation_Act_(Unite...

https://en.wikipedia.org/wiki/Single_transferable_vote#Unite...