Hey Ron! Here's my overly simplistic, probably erroneous take on Tenchi Nage. As far as removing slack from uke, I think If you source the two forces correctly (Aiki-sage and Aiki-age) it makes your partner unconciously "want" to hold on to your wrists. In the Aiki-sage hand you're basically leading their center into a hole behind them, which makes your wrist their main source of earth reference. Similarly, in the Aiki-age hand your center is basically driving up underneath them causing them to float which has the same basic effect of them relying on you for balance. As your arms spread out, uke's arms naturally have to spread out also, creating a connection across hos upper body?
For the breathing, as you take the first step you inhale to increase the pressure in the back bow for more power, and the pressure/connection in the arms and the upper cross. As you throw, exhaling adds more power by dropping the hara suddenly.
I think you're dead on about the open/close aspect. That's exactly how I see it, which could be bad news for you!
Again, just my two cents, and it may not even be that much!