The numbering and recommended levels can differ between the main, top and tall ovens. 'Second shelf' is ambiguous without its direction and cavity.
What the observation means
A cooking table may count from the bottom and refer to rail positions rather than the number of shelves currently fitted. Copying a position from one cavity to another can change the result.
A useful next step
Use the diagram for the cavity concerned and record the exact level in an enquiry. Do not add an unsupported shelf where a gap merely appears large enough. Secure, approved support matters as much as the selected height.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.