I have read the thread twice now and I still can't figure out whats causing me to go up only one point of CSR in FFA matches despite ranking 1st and 2nd most of the time. It seems impossible to rank up and when I take an L, I go down drastically.
Your CSR is at or slightly above the level of your MMR. Think of your MMR as your actual skill level with CSR being a visible gauge of that skill level.
Now let's say you are diamond 5 in FFA and your MMR is 1500, which is equal to being at the very beginning of onyx. So since the system is going to try to match your CSR to that MMR. Your CSR is equal to around 1400. So if you got in the top 3 in FFA you would go up 15 CSR while if you ended in the bottom 3 you would go down 1. Now your CSR has reached an acceptable range around 1500. However, you keep getting in the top 3 since it's harder to find people better than you since FFA has a low population. Your CSR now goes to 1550 by winning a lot of games and only getting 1 CSR.
However, throughout all those games you have been performing just like the average 1500 onyx player would in each match. So your MMR is still 1500 but your CSR is 1550. Therefore the system tries to bring your CSR down to your MMR by only giving you 1 CSR for a win and losing 15 for loss( top 3 and bottom 3 in FFA). That's fair since your skill level is only onyx 1500 so your rank shouldn't be inflated.
But let's say after a week of FFA you have gotten better and now you play like the average player with an MMR of 1600. Then your MMR will increase to 1600 quickly while your CSR goes up slower until you hit your new MMR at 1600. It could happen the same thing way but in the reverse direction if you play worse due to a break or you hurt your hand.
Also winning does not always increase your MMR more than a point or two since if you won but had a scoreline of an average onyx 1500 player then your skill level would be 1500.
If you want to rank up a considerable amount then you need to show the system that you perform on the same level as the average player of a higher skill. Yeah maybe you went 25 and 4 in that FFA, but if a player of your skill level was expected to do that and a player of higher skill would have gone 25 and 2 while also finishing the game 3 minutes earlier do you deserve the skill level you have or an increased one?