There ya go. Nakahiro's abilities are more mechanically based, focusing on power levels, reiatsu distribution, probably discerning specific abilities and how they operate, etc. Chiyoko's can focus on more widespread detection and more subtle things like emotions, aspects of personality maybe. Different abilities.
Also, on Michiko plot, Kina and Izumi should still meet at least before hand, or have met, I think. Obviously Izumi's sister can get her involved if that works for plot, but they should probably know each other.
Edit: Can my first post in a conversation not start a new page so I can read the rest of the conversation...?
Edit2: Confusion: Should Kina be in school on Sayaka's "First Day"?