I've just switched over from WinForms to wpf and in WinForms removing the whole title box is very simple, just set the title="" and ControlBox=false.

Now there's many suggestions on how to do this with wpf, all of them using native Win32 calls.
Although they do remove the control box, they still leave a thicker border at the top.

I'm certain it's doable using some kind of native call, but how?