Going by usual kpop logic, the one who stand in the middle when songs end play the role of "center"
This role can rotate but Garam is definitely the center for this song. She even stand in front when song starts. Same like Kyujin for Nmixx o.o people can argue all their way that Jinni is center too but honestly not convincing.
Chaewon has more center part because she has more lines - a given since she is literally the 2nd best vocalist in group + she is experienced