I make fundamental physics animations. I have to deal with a lot of circles - even one or two clicks less make my life easier 
And to clarify - that was just counterintuitive for me. If every other transformation works on both of them, why changing radius doesn’t? Now I know how it works and thank you both for clarification.
I don’t know why I didn’t try to mess with that handle but… It works! Thank you very much.
The last thing that I can’t solve is canvas and it’s properties. If my canvas is 400x400px and I import image made in Corel that’s 400x400px, I expect it will fit perfectly into the canvas. But it doesn’t, it’s bigger. I saw on Youtube tutorials that you have to mess with this Image Span property. Is there a value of that span that will make my Image Size and Image Area simply 1:1? I don’t really get the purpose of this image span…