Percentages are proportions.
180 damage on a character who has 360 health points in a life bar shows, and is, 50%.
180 damage on a character who has 240 health points in a life bar shows, and is, 75%.
These are both still 180 damage points. Identical damage.
Characters have TWO 360-point health bars, for a total of 720 health.
Aria has THREE 240-point health bars, for a total of 720 health. Again, identical.