The fixture and pump need a suitable arrangement for water to reach and leave the system. Available height and the product's approved application matter.
What the observation means
A pump capable of lifting discharge does not automatically solve every inlet-level problem. Existing slow drainage may involve the route before the unit.
A useful next step
Provide the shower and pump details for assessment without lifting the tray or altering hidden pipes. Do not assume a stronger pump is the answer or use repeated flooding tests to demonstrate the available fall.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.