That compares with what the French had measured:
15K trw downwind with spy asymmetric - 8.9K speed
15K trw 38º of trw - 7.2K
The speed downwind seems to be a bit worse but the French sailed with 15K ahd the Germans with 15/20K .
Did the explain what they mean by "downwind"? It would fit to the 180°-data from YACHT magazine.
Wave height was about half a metre...