ChristiaanJ
The only part I left off (arguably) is the part about the size and shape of the cone being relative to setting and configuration of the "system". This means velocity, and at velocities in excess of a specified value, the shape is as you describe. "Down the Rabbit Hole, Alice." I leave this hole at the end of every essay. One must allow the student some room to extrapolate, reason, and experience the "Aha!", No?
Arrogant enough?
Your water sheet on glass, was that in re: Laminar flow?
bear