Ken Yorke is a good friend of mine and a fellow rare breeder.
I suggest you read his article again as Ken does not say what you have written. If you read his article on his website there is another article following it written by Paul Russ in which he says he has bred DF Dom Pieds without iris rings but neither author states it is a fact for 100% of DF Dom Pieds.
Accept that some days you are the pigeon, and some days you are the statue.
Have bred all the currently recognised mutations including Brownwings, Darkwings, Saddleback, Faded and currently may have Dusk (to be confirmed).