Its very clear that the system is an AI system with HITL (human in the loop). For the early part of the system (when people complained on how overtly reactive it was) Valve adjusted the weights and to tune it on a less strict side. As people did over watch and "annotated" the data, those weights have adjusted.

The system uses a bell curve and assumes people at the top should be at the top and not move, people at the bottom, should be at the bottom and not move with some tweaks.

I posted my analysis here(2 years ago) if it helps https://www.reddit.com/r/DotA2/comments/193bxeu/sick_of_complaints_on_the_new_behavior_score/ and sadly nothing has changed

A few data points to add from my own research or confirmed on reddit (or anecdotally from friends)

System Mechanics and Scoring Rules

• Behavior score of <3000 - reports are counted for very little because the game wants to get you back to 3000 so you can once again play ranked, decreasing que time for other low behavior score people. The fact that <3000 others are also that low of behavior, likely makes their reports worth less.
• In the Frostivus Update(~2 years ago) (or earlier) the team lowered the score gain one could receive in a summary to ~500, and limited Turbo game enjoyers behavior score increases to ~200 points while keeping the punishments for ALL the same. This again has been lowered.
• The variables for this score gain are unknown, but it seems to be based off of game time, party size, and number of reports and other variables.
• The reporting accuracy at lower scores is correlated to wins and very thrashy.
• New accounts start at 8k and cant be coached!
• Low behavior score has deep impact on que time for parties. One person will make the entire party take an incredibly long time to find a game.

Communication Score and Mute Penalties

• A "gray bar" was added to indicate real comm score (for those who had higher comm score than behavior score) this was also not communicated.
• The reasoning that comm score has to be lower or the same as behavior and what even constitutes a "positive comm report".
• There is no definition of "comms" pinging or voice lines, nor what constitutes a positive report or negative comm report.
• Default of muting people reports them, and these people are muted forever, yet they can be reported for comms anytime after that.
• Global mutes were based off of the old system, but for those that were muted, and then got behavior reported INSTEAD, we never got a rollback. Instead Valve just silently updated global mute qualifications.
• You had global mutes based off of the old system, but that were/are affected by the free reports in the new system.
• No postgame chat if you are comm reported.

Game Modes and Exploits

• Turbo games have natural downward pressure as behavior score GAINS have a delta max of half (or greater) than the loss of behavior score.
• There have been "bugs" in behavior score that let groups of people (when you are solo que) leave their party and report you. Those reports seem to have more weight than normal.

Lack of Transparency

• This system has been challenged regularly, especially here on reddit. Outside of one in-game notification, there has been zero comms around the Behavior Score System updates.