Glass half filled with water, a paper is placed on it then the glass is flipped, paper doesn't fall, y??

i know when it’s full that the pressure of water acting on the paper is less than that of air from the other side
but when the glass is half full, air and water pressure act on the paper from inside the glass which makes that pressure > that of air yrt it doesn’t fall..

plz i want a very simple explaination (10 pts for the right and simplest answe)