Resize leading widget in flutter AppBar

I am making a custom AppBar that has a larger height than the typical AppBar. I would like to resize the leading widget/icon as well, and take advantage of the automaticallyImplyLeading default behaviors (so the menu icons and back icons are automatically implemented).

This is the solution I thought I would implement:

class AppAppBar extends PreferredSize{  AppAppBar(String title) : super(    preferredSize: Size.fromHeight(56.0),    child: AppBar(      centerTitle: true,      title: Text(title, style: textStyle)    )) {    (child as AppBar).leading =         SizedBox(width: 30.0, height: 30.0, child: (child as AppBar).leading);  }  static const textStyle = TextStyle(fontSize: 32.0);}

But of course this won't work because (child as AppBar).leading is final.

So in the AppBar below (text size made dramatically larger for illustration purposes), I would like to make the automatically added hamburger icon larger in comparison.

What do you think? Are there solutions for this or should I give up on the automatic icons and add them myself?

Edit: Added an image to show what I mean