Confusing coordinate position for arcs

[tythetasmaniantiger]

I've been trying to create diagrams that include concentric arcs. Here is an example:

Intuitively, I assumed that the coordinate position of an arc would be its center, but this does not appear to be the case. It took a lot more effort and "math" to arrange the arcs properly than I thought would be necessary for such a simple geometric relation. Is there an easy way to approach drawing (and editing) concentric arcs?