It doesn't, it's just a flat correction based on level difference between you and the enemy. If you're not doing Abyss I'd ague it's even more pointless to 90 a character, because the bigger the level gap, the more it would matter. You can nearly get 1 character from 0 to 80 for the Mora and Wits it takes to get one character from 80 to 90. Timestamped video for the level correction formula:
Levelling a character from 80 to 90 is basically the least efficient use of resources in the game. You can do it, but you'd get more out of doing literally anything else, including levelling a talent on that character.
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