Test Studio does not care what resolution you have your monitor set to. If 2560*1440 makes the text too small then I recommend lowering it to something readable.
However Test Studio does require that the browsers resolution be set to exactly 100% and the Display (aka DPI) also be set to exactly 100% as shown in the attached screen shot. Test Studio requires these settings to be at 100% because the calculations for mouse coordinates to click on assume that both are set to 100%. If these are not set to 100% the screen coordinate calculations will come out wrong causing mouse clicks to click at the wrong point, which obviously will make your test fail.