Funny thing, when I put my finger over the sensor it works, but when I put it on my ear during the call ithe screen stays on :/
Finally THE SOLUTION for less responsive top of the screen and proximity sensor!
There is a piece of black fabric glued in the upper part inside the case, covering the proximity sensor, front camera and the earpiece. I just removed it, cleaned the residue and VOILA! The screen is much more responsive, proximity sensor works like a charm. I am very happy. Never going to remove this case. Love love love