Why 'downloaded music' in music exceeds the 'optimise storage' size?

I have set the the option of 'Optimise Storage' to 16GB for my Music app in iOS.

My expectation is that, with the option 'Optimise Storage' on, the Music app will cap the storage to 16GB.

However the 'Downloaded Music' has taken up 40.21 GB.

Is my expectation incorrect? Or do I need to do something manually to bring the file usage down?

Currently my iphone usage is '242.7GB of 256GB'.

So I want to free up some storage.

If you tap on the "16GB" you'll see that this menu item defines "Minimum Storage", not Maximum.

It is used to define the amount of music you want to keep on your phones offline storage as a minimum, therefor giving you the option to have iOS optimize storage (delete locally cached items) in a different area (such as photos) first.