The mouse has to stop at the top of the menu bar, and not go into this void above the menu bar. The whole idea of the menu bar at the top of the screen is that it is an infinitely deep target for the mouse. You don't need to hit the menu exactly, rather you can fling the mouse to the top and it stops on it's own so you can click a menu.
This was a well-known interface and GUI design feature back in 1984 when the Mac was born.
This was a well-known interface and GUI design feature back in 1984 when the Mac was born.