While engraving with my 80 watt Chinese laser the laser power increases part way thru the process.
Try checking your machine bed, it could be that your focus is “more correct” further down your bed because it does not have the same height to the laser nozzle all the way. Your focus may also generally not be set properly. If all this is ok, then your power supply could be on its way in the eternal hunting grounds.
Gosh i hope not! This unit is new and already had to change out the board to a cohesion 3D and running smoothieware. Also having y axis trouble hanging up and skipping when running at a faster speed. Still troubleshooting that too.