LP gains/losses above highest rank held

I recently made it to Silver 3 which is my highest rank so far and saw my LP gains flatline even though I have above a 50% win rate. (around 54% currently). My placements put me in Bronze where I was gaining 25/26 LP per win and 17 LP per loss. Climbed to Silver 4 no problem. Once I got to Silver 3 it abruptly changed to gaining 17 LP per win and losing 17 LP per loss. My win rate has stayed roughly the same and the only thing that changed was that I exceeded my rank from last year.

I can understand if I climb higher and my win rate falls off. If my win rate stays the same and I maintain above 50% why do my LP gains dramatically take a nose dive? Because I exceeded my last year’s rank?