What is the history of the result that in a packing of the plane by unit disks, no Delaunay cell can be occupied by disk-sectors whose total measure exceeds $\pi/\sqrt{12}$ times the area of the cell?

I saw this in a two-page article that gave a nice simple proof, but (a) I can no longer locate the article, and (b) it was unclear to me when I read it whether the two authors (Taiwanese mathematicians, I think) were claiming that they were the first to prove the claim, or that their proof was significantly different from earlier proofs.