ELO score calculation inconsistency

[Nglob]

I won a Race for the Galaxy game recently (table 169949466), and was surprised how little my ELO rose. It looks like I got the average of the scores against the individual players instead of the sum of the scores.
OK, I figured they changed how ELO was calculated. But then I won a Splendor game (table 177072765) and the total ELO was the sum, as I had expected previously.
Does anyone know if this is a bug, or if the ELO calculation differs depending on the game, or what is going on?

[ufm]

Actually it needs some extra calculations.
Check this out and please upvote if current system is too confusing: https://boardgamearena.com/bug?id=29568

[postmans]

I also observed differences between Railroad Ink (where it seems average gain against all players) vs Welcome To (where it seems to be the sum of all ELO gains/losses).

Your example of race for the Galaxy vs splendor shows the same difference.

What ufm says about k-factor is also there, but is not accounting for all of the difference. in splendor you had a higher k-factor because it was still one of the first (20?) times you played that game.