Exactly: if implemented right and there's no gap between the menu and the top of the screen where the cursor does nothing, then you can just mostly jam the mouse in the general direction of the menu item.

Notably, Microsoft managed to bungle this initially in Windows with the task bar: there was a one-pixel gap between the buttons and the bottom of the screen, so you had to aim for the buttons or to readjust the cursor each time. (Though personally I find the downward motion more awkward anyway, both because the wrist action is weird and because the wrist and the wrist support are in the way.)

That's only one way. Don't forget about the return trip.