Struggling with scaling images using geometry reader

The above image is probably the best way for me to describe what I am trying to achieve. I would like the author's profile image to shrink as the user scrolls down, and then become the pinned header. Using geometry reader I was able to get the image to become larger while continuing to scroll up, but can't get it to scale down. Image will need a minimum size beyond which it won't scale down further even as the user continues to scroll down.

Any suggestions? Thanks!

Struggling with scaling images using geometry reader
 
 
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