I prefer not to use the term level, as CNC machines work fine on the Space Station …
What level helps with, is humans… it’s easy to put a level on the machine, but it has to be off enough for you visually see it with the standard level.
It should be clear that level isn’t a requirement.
What @NicholasL is driving at, is that it’s required that the machine be 3d square within it’s working area.
Sometimes a level is handy in helping you determine a problem … as long as you’re on terra firma, which is ok for most of us 
- properly working tube
- clean and aligned optics
- proper focus
If you have these three they work… any anomalies of poor performance can be any or all of these, but is very likely at least one of them.
Start at the beginning with a TEM00 mode check of the tube.
If you have a good tube, then follow with an alignment check/align… then a ramp test as @NicholasL suggested.
The depth of focus (dof) of a 2" lens is about 2.7mm (spot size is 205 microns) – a 4" lens is about 11mm (spot size is 410 microns).
This is based on a 6mm beam input, your 80W may have a larger beam resulting in a smaller dot or spot.
Good luck
