At small values of in-plane field Hp magnetic bubble domains can reside under charged walls at the edge of a nonimplanted disk. When H p is increased along the charged wall and exceeds a critical value Hpcrit1, the stable bubble position moves many microns away from the disk. The maximum gradient of the well along this direction also goes to zero at this value, but the apparent field well depth Hw goes to zero at a lower value Hpcrit2. Between Hpcrit1 and H pcrit2, Hw can actually be negative. A phenomenological theory is developed to show how this can occur. The maximum gradient of the well perpendicular to the charged wall is also studied. It is found to be asymmetric at low in-plane fields, to decrease with increasing in-plane field, and to be roughly a factor of two larger than the maximum gradient along the charged wall.