Hi,
I have been lurking and reading about all the work you are doing to grow iris. We have lived in a variety of areas from high mountain deserts to lowlands where winters were as cold as 25 below to 29 above.We never have bothered with soaking or refrigerating seeds. No matter where we lived we germinated our seed simply by letting the seed shrivel and shrink until about November/December. We then plant the dry seed in potting soil in pots. Placing a little gravel in the bottom to assist drainage, add the moist soil, push the seed in slightly and top with 1/2" pea gravel. The top gravel prevents frost heaving. The pots are then set out on plastic or sometimes a raised area and turned over to mother nature. In very dry areas one must add some water occasionally.  Klamath Falls has about 8 months of winter weather and can have a freeze any month. Yet we successfully germinated 1300 seeds one winter.
Hope this may help. And yes, we have very good germination.
Maybe Mother Nature knows best?  You might give it a try.
Vicki