Stored items and the shelf material may be exposed to heat or obstruct the intended space around cooking. The cooker's installation instructions must govern clearance.
What the observation means
A shelf can also encourage reaching over hot pans or flames. A decorative change can therefore alter practical safety even when it does not touch the appliance.
A useful next step
Discuss the proposed arrangement with a competent installer before making changes. If an existing shelf shows heat damage, stop using the cooker until the concern is addressed. Do not treat a larger extractor as automatic permission to reduce clearances.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.