Thanks so much for the detailed analysis. Just had a chat with the bike shop mechanic and he said both Birdy and the new Dahon K3 Plus have the same situation with the front brake disc on the right side. He said that the Shimano Ice Tech disc can only be installed in one direction and cannot be flipped over. But he emphasised that for Shimano’s disc (the one that I am using is exactly RT86), it’s fine for it to be rotated ‘backwards’, however, for Hope’s brake disc, he would recommend to flip it over (and it can be flipped over) to retain the direction of rotation.

Hope’s brake disc