Thank you, Robert, also thanks Chris, to whom I must offer an apology - I have found the answer under my nose, in the relevant Jane's entry -
'A small aerofoil surface is mounted above the leading-edge surface of the top wing, behind the pilot's cockpit, to correct the flow of air disturbed by the cockpit opening.' (the notion of French designers of the period being concerned about airflow is somewhat hilarious....)
but thank you anyway for posting that splendid document - it never ceases to amaze me what is out there......
Back, inevitably, to the water -