Yay! Irimi Nage thread!
I guess a follow-up question from me would be - who focuses on off balancing uke via their head and who does it via their upper body?
My answer is... yes...by which I mean....when I first enter, I want to draw uke forward so he is slightly weighted onto/in front of his front foot - so I guess that would be initial entry is balance break via upper body, although I am considering it simply attaching to uke and adjusting my structure rather than pushing uke forward. Once I start to move, I try to keep a balance in my own structure between my hand which is attached to uke's head and slowly guiding it towards my opposite shoulder - and my other hand which is attached to uke's arm and using that connection to get his center past my center...however, in practice, I've been getting feedback from partners sensitive enough to notice that I tend to overplay the hand-at-head.
So back to try another day :-) Fortunately what we call shomenuchi kokyunage (most folks' iriminage ura version but without the down-to-mat faceplant thingie) is part of "8 basics" so we do it pretty much every class at least four times each!