It may require a separate permitted selection. The inner and outer heating areas are not necessarily active together at every setting.
What the observation means
The control sequence varies and should not be guessed by forcing a knob beyond its stop. A visibly dark area alone is not proof that the outer element has failed.
A useful next step
Check the model's dual-zone instructions and use cookware of the appropriate size. If the outer area remains ineffective under the correct selection, record that result. Do not touch the glass or dismantle the surface to compare heat.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.