1080p getting "low" FPS count

Hi there!,

Backstory -YOU CAN SKIP THIS PART-

'I'm upgrading my PC. So I left my "old" PC for my wife. My wife didn't want a 27'' inches screen because she was using a laptop before and she rather had a smaller screen and I bought a new one but 144hz for me, so I asked a friend who was interested on buying my screen if he would want to swap screen with his 23'' inches with no extra money. He obviously accepted and came the very same day, even though I still didn't have my new PC. I said to him that I didn't mind to do it that way'

So I had this PC:

Intel 4790K 16GB RAM Corsair Vengeance Pro GTX 1070

League was running at 230 FPS+- at 1440p on my screen.

I've downgraded my screen to a 1080p (see Backstory) under the same hardware

Theoretically my GPU should render more frames by down scaling from 1440p to 1080p, but this wasn't the case. And I would get 210+- FPS at 1080p. Just calculating on raw proportional scaling, it should work at approximately 325+- FPS, since it's rendering 43% less pixels than 1440p.

Also I remember running League 1080p with my GTX 560 at 400 FPS+- but I guess it was on an older version of Legues' graphics engine.

Can someone tell me what's going on?