[UlfSchmidt]

3. Yes, as per design. I use a logic which takes 3% but at least a radius of 6. Otherwise you cannot see the radius for small images. I wanted to make the redius visible also for small thumbs. I find that in line with other implementations I saw.

This brings me back to one of my previous postings:
I find the rounded corners particularly disturbing in lists where one icon is directly placed after the other without any blank space, like it is done in list views. No big issue for grid view, but yes, please limit the amount of the rounding.
So maybe you can at least once try to remove the rounded corners from the list views completely, so we can see how this looks in real life. And you do not have to touch the playlist view. A big bonus!