Thank you for visiting and your comments, the white overpainting is made by brush, following the pictures on the instruction manual and WNW website. My opinion after several hours looking is that of a kind of pattern in the winter camouflage, broken by inflating - deflating of fabric skin during flight.
About the compass location, I suspect the aeroplane was used for cartography or artillery direction. I was tempted to insert another compass inside the cockpit, as it's unbelievable the pilot was flying under directions from the observer. But it's speculative, so anithing can fit...
Ciao
Giuseppe