LG 31MU97 4K Display In Full 4k letters are shown unclear

I just bought this LG 31" 4K Display

F.e. the Browser Tabs, there it is much harder to read compare to an 27" thunderbold Display.

If i go to the middle 2560 x 1350 then it is all good and fine, but that is more or less the same than the 27" has already.

Does anybody have an idea how to use the 4K option in a way that lines are perfect and letters are as clear as on a Thunderbold Display?

1. picture is with the 4k (you can see the lines looks on the bottom bigger than on top.

2. picture is with the Thunderbold 27"