I have a different brand of laser but I have found that, indeed, focusing is critical for correct operation.
It’s not very difficult: first decide whether you need a broad beam (faster for text but less crisp) or a narrow beam (ideal for cutting). Then set the laser height roughly with the manufacturer guide.
Finally create and engrave a test pattern (see this video), by varying the Z axis until you have the result you are hoping for.
Again, I don’t know about the JTech but in the case of my Opt Laser, the lens turns to focus (like a camera lens) the beam and so the lens is loose. If the JTech supports focusing the lens, proceed with small movements, an 1/8 of a turn at a time! But first check their manual first to see whether they support focusing the lens.
my bad, I just found out that the little chrome ring around the laser isn’t for fastening but it actually is a focus ring. that i I shouldn’t F*$#% with