"Import" watts tend not to be real watts!!! Because the Z80_8W450B9 laser diode is a multi-mode diode you will always get a rectangular spot as opposed to a symmetrical dot. This is a characteristic of multi-mode laser diodes.You want to focus it so you have the cleanest and thinnest line possible. Don't try to make it symmetrical or you will produce a larger and less powerful spot.
Be aware that the closer you get it to the work the more likely you are to get smoke and/or soot on the lens. It can be cleaned with a very soft.