How does it work? I changed the element size from 2mm to 1.5mm and the FOS actually increased(when previously it had decreased)
You have to do a mesh convergence analysis: you need to decrease element size untill your solution will not change, that means you are getting something close to reality, in any other cases you are playing with something unpredictable. And yes, smaller the element size=better the result in very smooth conditions. BUT in case of stress concentrator it is NOT, you have to have a right skills to spot the all stress concentrators, mesh them properly and do a specific procedure to extract real values out of calculated.