Here's the thing about the circle exercise: it has to be what really is; it can't be what we wish it could be.
Actually, it might be a worthwhile exercise to make a "wish circle chart" where we put people/relationships where we'd really like them to be on the circle. That kind of chart would give us a chance to ask ourselves what, if anything, we could do to get those relationships to the circle we wish they were in.
But when we are making a circle chart (not a "wish" circle chart) our job is to be scrupulously honest. (It's important to note that all of us get to define the characteristics/criteria of/for each circle, and that we might each define the circles a bit differently. In general, though, the more inner the circle the more truthful,vulnerable, honest the relationship is.)
For instance, Runforjoy, you may wish your mother could be in the innermost circle; whether the relationship with her truly meets the criteria for residing there is another matter. Only you can assess where that particular relationship sits on the chart, and, if it doesn't sit where you want it to, whether there are any changes that can be made to move it to where you'd most like it to be (sometimes we can make changes, sometimes there's nothing we can do- in relationships like those we talk about on this blog it generally takes both parties to effect change).
The circle chart ends up being illustrative and helpful. It also can be illustrative and evoke sadness, disappointment and/or grief. I tend to think the helpfulness of it creating it outweighs any potential discomfort that come as a result.