They can be so dramatic in a mass planting.. I've often had good intentions of doing just that... somehow, the collector in me takes over, and the best I can do is broad drifts of one.
Oh, actually I did have a mass planting of 'Crimson King' a few years back. It's been chipped away at until it's just a single clump now.. Sadly, 'Crimson King' has been the only Iris that has really thrived in that bed, for whatever reason.
the following year, the clump started getting smaller