I think Dee is likely right. Honestly, I don't know of a definitive way of separating them. I've grown I. suaveolens for ten years, and I.p.subsp. attica for only five years. Assuming the identities are correct, the noticeable differences is overall size of the plant (attica is larger) and length of the floral tube (in proportion, much longer in attica). Growth patterns are very susceptible to environmental characteristics. They need really harsh conditions to get the well formed, falcate leaves... dry soil, absolutely NO crowding, lots of air and lots of sun. Both species are evergreen (even in zone 4). Falls have a stronger tendency to turn under with suaveolens, as you might expect. When you deal with species, there is always so much variation that may occur. In my pics above, I. suaveolens grows actually grows in less harsh conditions than attica.
