I don’t have a perfect fix, however: you can specific the base icon differently for iOS and Android. Read for example: https://blog.ionicframework.com/automating-icons-and-splash-screens/ (basically, instead of putting icon.png in /resources, put two different ones in /resources/ios and /resources/android, and fool with the Android one until you get what you want. Might involve making the icon expand to overfill the image you provide…
Somehow you specify android:icon and android:roundIcon
Do we know if Ionic/Cordova has a setting for round icons vs not round. As we see in screenshots like that not all of the icons are round some people are still using a square one.