It's hard for me to explain it but I guess I feel like Kurogane is too... all knowing?
Like, when Mamakura first came to Kiseki, Kurogane knew right away that she wasn't the princess he knew. But Mamakura and Paparan are supposed to look just like Syaoran and Sakura. He's an observant guy, but I found that hard to believe. In fact, with the doubles he seems to be able to tell right away; with the Fais its different because of the eye-patch and also one being his soulmate, but with characters he may not know very well, and especially when they first arrive to Kiseki, he seems to be able to tell right away that something's "different", despite them communicating through journals and only responding one or two comments before he gets it.
And same with little Kurogane, when he posted an entry that amounted to only "hn", Kurogane seemed to know right away that something had happened between him and the little Fais(or at least it seemed that way.) And it's just hard to believe that he would be THAT observant, despite the fact that it isn't too far-fetched.
I guess what I'm trying to say is that yes, Kurogane is observant, but I think that you're making him SO observant that it just seems silly and that you're letting your ooc knowledge move into how you play him.