LP gain going down?

It is based on the elo of people who you win / lose against.

LP gain/loss is based off of MMR. You get more LP if you are playing against people where you have higher MMR, and less if you are playing against people where you have lower. This is because the system wants to stabilize you at ~18 LP loss/gain, playing against people with equal MMR, so if you are consistently outperforming your opponents and keep winning, your MMR would go up, and so would LP gain. From my understanding, the system tries to find a balance between MMR and div/tier when matchmaking, so once you get to the tier that matches your MMR, you will find LP gains roughly equal to losses. As a side note, MMR begins to exponentially decrease/increase as you go on loss/win streaks. A good site for checking your MMR, if interested, would be OP.gg

Okay I see, I thought gains were based off of personal MMR.