[shrike]

You're right, a helmet cowl's main purpose is to force air through and around the cylinder, although it also cuts down on drag by presenting a much more streamlined shape to the airflow. Modern pressure cowls, especially on narrow airplane like F1's are very similar, although longer to accommodate 2 cylinders inline. (see blurry light coloured photo below for a helmet cowled radial)

The cylinders on the Avia have fairing behind the cylinders.(see darker photo in Super Fault Finding Macro Mode) This came into and out of vogue very quickly immediately before the Townsend ring was developed. The Bristol Bulldog is the only other airplane I recall making it to production with them.