Interesting. My android's barcode scanner can read the regular size but not the micro size and I tried multiple scanners. I'd like to see what it manually takes to read these as well.
I like your rendition better though...LOL
How QR codes are made.
Here is an article how to create a level 1 QR code. http://www.swetake.com/qr/qr1_en.html I guess micro QR will work the same way.
If you want to decode it, just do the same in reverse order. A large portion of the article is about error correcting codes and verification checksums. Little bit of math, but you don't need that, since you will be decoding a QR code that is not damaged.
I say embed the coin with a microchip like they have for animals, then maybe they won't get lost :D