A large item can shield other surfaces or interfere with a spray arm when positioned poorly. The loading arrangement matters as well as the overall quantity.
Understanding this situation
Use the model's guide for pans, trays and bulky cookware. An item fitting inside the cabinet does not mean it leaves the intended water route clear, particularly under an upper rack.
A useful next step
Rearrange suitable items before starting and check movement only with the machine stopped as the manual permits. Do not remove a spray arm simply to fit a larger pan. Describe repeatable poor-result areas if a sensible load still washes unevenly.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.