Soo my farm lategame is kinda uh bad

So I was looking on league of graphs to see my farm and stuff. For the first 10 minutes, I am on equal footing in cs vs the average player in my rank. Then by 30 minutes, I am 30 cs down from the average player in my rank. 30 doesn't sound like a lot, but that's consistently over like 500 games. This is only statistics for one champion btw. I feel like I don't know when I am supposed to farm after laning phase.

You can see the graph I am talking about if u go to Galaxy Fighter profile on https://www.leagueofgraphs.com/ make sure to click Vladimir