QGraphicsview - how to organize scene and items

[metRo_]

Hi,
I'm developing a joystick for mobile but my questions is not about the code itself but how to organize it.

This is what I have:
7572

And is organized that way:
7573

That way I noticed that I need to hardcoded a lot of values because I don't have information about the bigger circles (limit for small pads). I'm thinking in change that and these big circles be a scene or a qgraphicsellipseitem inside the joystick class.

Basically I want you to suggest how do you change this.

Thanks :)