The honeycomb grid panel doesn’t have a perfectly flat surface, but the bench block kinda sorta averages things out:
I jogged the platform down until the nozzle just cleared the block, then measured the space at various spots across the grid. Somewhat to my surprise, it’s just about as good as you can expect:
You could argue that the left side is lower by half a millimeter.
The four stout single-start leadscrews moving the platform have a 4 mm lead (= pitch for single-start), driven by a belt with a 0.2 inch (!!) tooth spacing around 14 tooth sprockets, so moving the belt by one tooth produces 0.286 mm of vertical motion. I could loosen the belt and turn the left rear leadscrew one tooth to raise that corner, but not right now.
The laser lens has enough depth of field to cover a millimeter without too much spot size variation, unless you’re being very fussy. A quick focus check:
The center hole happened pretty close to the lens focal point, with the adjacent holes 1 mm above / below that point. An accurate initial focus setting is obviously important, but varying by half a millimeter on either side seems survivable.