I recently picked up a used chinese laser which is a 120 watt nice cut machine. Seems pretty decent for the $. It came aligned from the previous owner but I am not totally sure he knew what he was doing 100%.

My question is this, I was able to cut through in 1 passes at 80% power a piece of 1/2" MDF no problem near the top of the table. So after doing a test piece of about 8"x8" I scaled the drawing and cut up to 24" to the size the customer wants. I ran the same speed and same power and all the cuts near the top 1/2 of the table are fully through the piece. However near the bottom half they are about 1 to 2mm shallower in cut. Would this be caused by an alignment issue of the mirrors not focusing as much power at the lower points of the table?