Did a little reading in 'The World of Irises' after lunch & EC does come from the amoena pattern. Emma Cook itself was listed as have rather pinkish line around the falls. Paul Cook in the 1950s produced dominant amoenas. Another book on hybridizing mentions that EC has an inhibitor for blue which
produces color as a narrow band around the falls.
OK Tom, while you are hybridizing why not produce some Emma Cooks. They might be seen as a narrow tutu.