A fan does not make every location identical for every food. Shelf position affects exposure to heat and space around the tray, especially near a grill or cavity wall.
What the observation means
Packet directions may refer to a middle shelf, a preheated oven or a particular mode. Combining those directions with a different shelf and a crowded cavity changes several conditions at once. The oven's manual may provide a better model-specific equivalent, but the adjustment should be deliberate rather than accidental.
A useful next step
Follow compatible packet and appliance instructions and retain the actual shelf level if the result is poor. Remember that some manuals number shelves from the bottom. If the selected level and mode are correct but the result has changed abruptly, describe that consistency. Do not use the cavity floor as an extra shelf.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.