Android Studio
when you using android studios "Image Asset Studio" for generating the app icons by using the Icon Type: Launcher Icons (Adaptive and Legacy), it will give you a preview on how the App Icon will look in different formats and sizes. See attached Sources: https://developer.android.com/codelabs/basic-android-kotlin-compose-training-change-app-icon#0
https://medium.com/google-design/designing-adaptive-icons-515af294c783
This should help you determine your desired result.
Flutter Launcher Icons
Also when using your mentioned package: https://pub.dev/packages/flutter_launcher_icons
It also provides configuration options for adaptive icons. Please see attached source: https://pub.dev/documentation/flutter_launcher_icons/latest/
adaptive_icon_foreground: The image asset which will be used for the icon foreground of the adaptive icon Note: Adaptive Icons will only be generated when both adaptive_icon_background and adaptive_icon_foreground are specified. (the image_path is not automatically taken as foreground)
adaptive_icon_foreground_inset: This is used to add padding (in %) to the foreground icon when generating an adaptive icon. The default value is 16.
adaptive_icon_monochrome: The image asset which will be used for the icon foreground of the Android 13+ themed icon. For more information see Android Adaptive Icons