<…>
Could you explain the simple colorful calculation you made?
By the looks of it, it was, with regards to @suchmoon’s data: add 3 to Brand New, subtract 3 from Newbie, and finally wipeout altogether the Hero rank (not present).
<…>
The Average post per active user and rank, along with the % of active users are the most interesting ratios. One thing that I wasn't expecting is Jr. Members (19,83) to have an average posting per month that less than half of that of Heroes (49) and Legendries (40,32).
Newbies apparent low average posts per month ratio (7,62) is likely diluted amongst a large standard deviation. That is, there are likely many Newbie accounts that have posted very few posts, and a smaller (yet visible) set that have posted a lot. The former group, being likely larger, drives down the average a fair share.
I created some similar ratios back in early December 2018, and the ratios do seem to differ somewhat, specially on the Jr. Rank level (see
Analysis – net posts created/destroyed in a month per rank).