SetFromSingleQualityLevel has different behaviors

I’m using this c++ code to change graphics quality:

GEngine->GameUserSettings->ScalabilityQuality.SetFromSingleQualityLevel(aValue);

GEngine->GameUserSettings->ApplySettings();

GEngine->GameUserSettings->SaveSettings();

If I change graphics from Low to Epic, the result will be diferrent from High to Epic change (High->Epic change gives better quality).

Why is that happening and how can I solve it?

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Still active