I wanted to test center recognition, and it seems like if you don't have a girl at the very front of the formation but two in the 2nd row, the game selects one of the two to be sole center as marked in the singles/jobs tooltips, but it doesn't count for the "center a single" wish. Maybe the game could add WCenter mechanic? (ie if there's not a girl at the tip of the formation, the girls in the second row are centers. Or even better, a second formation option that allows 1/2/4 centers, ala a 5-6-5 formation:
x x x x x
x x x x x x
x x x x x