Clarification on Mion roleplaying as Shion?

[Belm]

I'm having difficulty concerning Mion/Shion characters since both can basically switch places as explained in the wiki regarding Sonozaki heir's Tattoo in which the current Mion had (Shion by birthright) Things so far :

Angel Mort with Dad It's 50% Mion being too flustered to reveal herself to Keichi

Delivering Lunch Box The delivery timing and chapter tips suggest that it's Mion

Keiichi in a pinch Shion wasn't present during the Hinamizawa dam fight. The whole conversation about the solidarity things afterwards also point out to Mion

Spoilers are welcome

[GuppyForce]

All of this is revealed in Ch. 5 Meakashi