I am quite literate regarding RPI (and BCS) having been considered as a "guru" in both in the past.
Both have become less relevant in recent years, which is why I seldom comment on them anymore.
If you have questions about the legitimacy of either metric, I'd be happy to respond.
Ask away. I won't be held to a timetable as to when I might respond, however.
I do have my own life to live.