This time, the Image Level is decided based on the base statistics of the unit.
In other words, unlike in previous games, even if you raise the statistics as much as you can using costumes and accessories, the Image Level will not increase.
Every basic statistic's maximum is about 60% of the maximum for the bar. Below is a picture for reference.
It reaches to about the 16th dot on the dotted line below the statistics.
Unit Statistics >