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: iOS: Can't change height of ion-header-bar
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.