When the same job is darker, lighter, deeper or weaker depending on bed position, changing power first hides useful evidence. Use one small controlled pattern and move it around the work area without changing speed, power, focus method or layer settings.
Build a position comparison
Test at the center and near each corner on one sheet. Label every result by position. If possible, rotate the sheet and repeat. A defect that follows the material points toward grain, coating, moisture, contamination or thickness. A defect that stays at the same machine position points toward focus height, bed geometry, optics or beam delivery.
Measure the surface, not only the frame
Warped stock and uneven thickness change the distance to the lens. Check that the material is supported safely and lies flat. Measure the nozzle-to-surface or approved focus reference at each test point. If the distance changes, correct the bed, support or material before tuning speed and power. Do not place unapproved weights or reflective objects in the beam path.
Inspect optics and alignment safely
Dirty optics reduce output and can create heat damage. Clean only with the procedure and materials specified by the manufacturer. For machines with a guided beam path, follow the manufacturer alignment test at multiple positions. Do not look into the beam path or defeat the enclosure. A gantry that is not square or level can also change focus across the travel.