Having established that the laser beam comes out of the lens perpendicular to the honeycomb platform surface, this seemed peculiar:
The mirror 3 + lens tube has a distinct tilt when seen from the +X direction (the right side of the machine, so it’s in the YZ plane, I suppose).
This is not matched when seen from the -Y direction (front):
The tilt does not seen to correct for a misalignment in the X axis rail or the brackets attaching the head to the linear bearing.
The beam seems properly centered on the lens and nozzle, so I’m loath to twiddle the alignment just to see what happens. One of these days, for sure, that must happen …
The Smell of Molten Projects in the Morning 
Looking carefully at your photo, I have the impression that the tube from the lens to the nozzle is perpendicular (well, logically it must be since I expect the hole for the air assist is too small to allow that dgeree of tilt) – so is the upper mirror block compensating for a badly seated mirror. And is the mirror block to tube badly connected?
I bought my laser cutter (a 40W model) second hand just before yours arrived so pleased to have your ideas appearing in a timely manner!
Simon in France
The tube really is perpendicular to the bottom face of the mirror block: the whole thing sits at that angle. I wrapped shim stock around the top of the lower tube to improve the collet’s grip on it, although the beam remained neatly centered in the nozzle opening.
I must tear the whole thing apart to find out what’s going on in there, but as long as the beam comes out the hole, that urge stays wrestled to the mat.
Oh, and give my regards to Ms Thompson and her twin sister Ms. Ipsum over in sales … [grin]