I see that Wan is apologising on another site that he has made the grid-stare too hard. I have found one of the type of things required, but am at a loss to find any others (which all must be as unusual as the 3 in the across clues), nit sure how to interpret overlapping and mirror symmetry. Is each pair mirror-symmetrical, or merely the whole thing? And is overlapping like this: greecegypthailandenmark or something else? I know the shape I'm looking for, but even drawing a rough set of the right number of cells doesn't produce any glimmer of light. Oh dear!