How do I show margin and padding values?

I'm writing an application to create road signs (it won't be obvious to most people), and a certain interaction involves the user clicking an object on the workspace (in this case the text "Newmarket", labeled 5), and the window labeled (6) appearing to provide a means to edit data.

These objects have certain properties such as margin or padding (or in some cases corner radius and border width), and I don't know if the diagram I have in the bottom half of (6) presents the data intuitively to the user. Does this design work, or is there a better way to do it?