The top left corner of my forge seemingly loses some juice in the top left corner. The photo is the flipped cut.
I would first check and clean the window under the left hand side of the lid and look hard (post a photo of ) the window on the side of the head. It is rare for there to be a difference between top and bottom, but not so much that the right side will fade compared to the left.
Two things can cause this. Either the beam gets fuzzier as the head moves right dure to dirt etc. or (mostly on new machines) the laser beam is not perfectly centered on the window of the head due to rough treatment in shipping. In either case the beam is less messed up between the two windows when close but gets more so as the head is farther away.
Well thank you for the knowledge.