What is this air-scoop behind the cockpit of the Polikarpov I-153 and Stearman?
(Source)

The F1 air-scoop / airbox is well clear of the driver's head to feed air into the engine (the airbox itself is shaped so that each cylinder gets equal share of air).

In your 3-view diagram, that's a streamlined headrest for drag reduction.

The I-153 has a top speed of 444 km/h (243 knots, 280 mph), whereas such streamlining is not needed for the leisurely paced Tiger Moth, for example.

Googling photographs makes it clear, unlike that line drawing.

(Source) Click to view.