Prince Leios sure is persistent, but think he misunderstood Sayaka showing where she came from with how they dressed normally.
Maybe Kou and Sayaka were together on that plane accident, seeing her in the school uniform might unoick his memory.
Kou forgot how they fought in a team during bandit arc, rushing head first revealed him as a trump card and already focused attention to Lef as his supposed controller. Opposing team will probably "jinx" Lef I'm afraid.
For a secret experiment, a lot of people know too many details around Kou's golem.