Both my monitors are actually TVs where I plug my PC. I checked input lag, my current TV has 27ms. There's a Game Mode option to reduce this, but it didn't seem to make any difference. Anyway, I didn't find info on input lag of my previous TV, but a similar model had 44ms, so I'm not sure if that is the issue.
Well, thanks for the reply though, I just wanted to check if it could be some bug. I'll see what I can do to adapt myself, I don't wanna lower the difficulty level.
EDIT: I take back what I said. It seems Game Mode actually made a difference. I just beat Chela 6-2 in same surface as before
It seems, according to my google research, that 27ms is the input lag with Game Mode ON. When it is off, the lag is around 115ms. That's probably why I wasn't reaching most balls lol.