According to the dev post on SR gains and matchmaking. The SR gains for performing well are a ‘small modification’.
This makes sense as one particularly good game does not indicate higher overall skill, consistent overperforming however indicates a player might be misplaced.
The SR modification being small means that it adds up over many games allowing you to get to your true rank faster than without it. If the boost was too big then players would constantly overshoot their rank when they play better than normal or drop too low when they play worse than normal.