Leave the iris flat. It's easier to morph a convex/concave from a flat than vice versa. Concave is a hack to give the illusion of refraction. Not necessary. A tiny bit of conconvity is fine, otherwise it's just more of a PITA.

I'm hoping you welded the iris to the sclera... Creating Iris morphs are nearly impossible, or extremely more difficult, otherwise. Having unwelded parts to an eyeball makes 0 sense. It just introduces problems and solves none.