Yes, this is from a while back, but for anyone else reading this/finding it through Google, I would argue that this is not the correct way to go. Use the SASS variables to do this properly.
$bar-height: 80px
More info here: https://forum.ionicframework.com/t/ios-cant-change-height-of-ion-header-bar/11477/4
However, if you cant use the SASS files, then you may be forced to 'hack/over-ride' it as suggested above.
But I would highly recommend doing it using the SASS variables.