What did he place on the Mitznefes? Why can it not have been the Tzitz?
1.
Rashi: It was the Techeiles thread that he placed on the Mitznefes as a sort of crown.
1
It cannot have been the Tzitz, because the Kohen Gadol wore his Tefilin
2
between the Tzitz (which was placed on his forehead) and the Mitznefes.
3