Your position dot looks to me like it's in the right place to be the "balloon flaw."
The cancellation would knock down the value, somewhat. But I'd say that you found it.
Here's a scan of mine, next to the illustration. As a note, mine has a cert from the Green Foundation affirming the ID of the flaw.
Also, if you go back to the beginning of the Large Queens listing in the Unitrade catalog, you'll see that the "standard" perforation gauge for the whole series is 12 x 12. However, the 15c grey can come in both 12 x 12 and 11.5 x 12, as denoted in the second line of the listing.
Chip
