title: How to get the SliverPersistentHeader to "overgrow"
body: <p>I'm using a <code>SliverPersistentHeader</code> in my <code>CustomScrollView</code> to have a persistent header that shrinks and grows when the user scrolls, but when it reaches its maximum size it feels a bit stiff since it doesn't "overgrow".</p>
  
  <p>Here is a video of the behaviour I want (from the Spotify app) and the behaviour I have:</p>
  
  <p><img src="https://media.giphy.com/media/gIlT8fvBCWhvpoc9v0/giphy.gif" alt="Video of behaviour">.</p>