As I understand it, as long as there are no players with ‘provisional’ ratings in the room, then the only variables that matter are your own rating and the average of all the other players’ ratings (i.e. your opponents’ ratings are not considered individually).

e.g. say you are rated 1650 and your opponents ratings are 1700, 1300, 1300, 1250 and 1050 (a diamond 4, two gold 2s, a gold 1 and a silver 3, not that uncommon a situation to be matched into). Your expected position based on those ratings considered individually might be second.

But the important value is the average opponent rating, which in this case is 1340.

Per the Elo formula this gives an expected performance value of:

1 / ( 1 + 10 ^[ {1340 - 1650} / 400 ] )

= ~0.856

[1 divided by 1 plus 10 to the power of the average opponent rating minus your rating over 400]

which in a 6 player room corresponds to a result between second and first; meaning the rating system takes points off you for finishing second, though the scale of the penalty is lesser than the scale of the reward for finishing first.

I believe the K factor CFP uses is 30 so for each possible poisition your rating change would be:

1st : +4.31

2nd : -1.69

3rd : -7.69

4th : -13.69

5th : -19.69

6th : -25.69

(if you want to play around with this I made a google sheet; just change the values in the pink cells and it’ll do the rest for you - https://docs.google.com/spreadsheets/d/1dM5hnpcBYJTmROc6wuHDAnp3eB6Wvd7Cn7UDkwDKA9M/edit?usp=sharing)

For the most part I think this system is pretty good and fairly equitable, however it does throw up some weird oddities.

For instance [assuming the K-factor is the same across all room sizes], you would gain more points by finishing first in a room against one diamond 2 and three bronzes than if a fourth bronze joined to make it a 6-player game, due to their disproportionate effect of pulling the overall average rating down.

If anyone with knowledge of the rating algorithm wants to correct me on any of this, feel free to of course!

But I hope this should explain how they work in a bit more detail to those who are curious and who have a bit of maths knowledge.