Christian and Charlie ... I appreciate your responses. Heck my teachers say the same thing in regards to cutting down. What I'm trying to pick at here is what happens on contact, if you manage to actually connect with nage's head with shomenuchi. Although my intent is to make contact and cut down, my striking arm will extend forward (however little) to prevent it from collapsing before continuing down (so basically, a push). If nage removes the target, the strike will follow-through and continue down to resemble the "correct" form of shomenuchi.
the attack becomes more of a push than a cut if you don't strike to the center making it much harder to generate power in the attack.
Cutting down or not, It is always my intention to strike the center, if not "to" it. A "push" with downward intent can be quite powerful.
I would like to take more time to write more clearly on what I mean (and to get to my elusive point of where ikkyo/nikyo fits in), but I have to leave work and get home.