Andrew R Stewart
Perhaps the picture of the front caliper and rotor does not fully convey the issue, but the amount of unused surface area is significantly greater than the thickness of the ball-and-socket washers. I did write somewhere in the middle of my admittedly TL;DR post that I tried doing away with the convex washers and mounting the caliper directly to the adapter. I also wrote that that brought the caliper in contact with the fork, making it impossible to secure to the adapter, not to mention getting it aligned.

And when I wrote "BB5-based" I meant that the calipers that Dahon chose to specify for this bike use Avid's BB5 pad design standard. Apparently, BB5 pads are some of the most popular ones in the world. With the possible exception of Swisssstop, every aftermarket manufacturer, from Galfer to Jagwire to about a zillion Chinese brands that I couldn't even pronounce, have "BB5" pads in their product lines (most of them don't even bother to mention "Avid.")

You ask if my original calipers had been made by Avid, and I couldn't tell you if they were. I could not find the actual brand or manufacturer's name anywhere on my bike's calipers - just a couple of mold numbers and a lot of casting parting lines. For all I know, Dahon probably couldn't source any quality calipers from any of the name-brand manufacturers in the middle of the universal COVID parts shortage, so they went with whatever they could get their hands on at the time.

Or maybe they were just penny-pinching, having struck some kind of deal for $2.99 apiece or something. In any case, all I know is that there wasn't much I could do to achieve any meaningful improvement in the performance of the my original brakes. I guess an upgrade was very much in order.