Hey read this thread I made about the secrets of Minato (father) and Naruto (son) KCM;::;;;
You must be registered for see links
Did you notice that in the Picture, Minato's seal is from under (i.e. upside down), whereas Naruto's seal is from the top.
I think it's because of how Minato sealed it, Yin is the first half which is u'shaped on Minato's stomach or chest, which Yang is the second half which is n'shaped... together they will make a whole YIN YANG Kurama chakra, so I dont believe it when people say that KURAMA has regained his Yin chakra all these years in Naruto. However when Naruto unluck the seal he looks super cool and it becomes round.