As I mentioned before, the beam is not quite round. When it's not focused properly, it magnifies the ratio. The shorter the focal distance is, it's harder to focus and it's not as tolerant if your material is not quite flat.
If you raise the laser out of focus you will see the laser's beam is a rectangular shape. Rotate the laser module in the heat sink until the long side of the rectangular beam shape is parallel with either the 45 Left or 45 right engraving angle. Then set the focal distance at 3.00" from the heat sink bottom face to the top of a piece of black anodized aluminum placed on the X-Carve's bed. Focus the laser beam to the smallest focal point as possible. Then secure the lens in place so it will not move by dabbing some hot melt glue a few places from the lens thread to the laser module. Only engrave at the 45 degree angle you rotated the beam to.