After reading the (very interesting) discussion, I had another look at Janet's question to see what else I could pick out.
Janet Rosen wrote:
If I give the kind of very focussed intent attack empty hand that I'd be giving in partnered weapons work, I'm bringing a certain solidity to it, a feeling that I will reach my goal with my center/posture intact. If nage moves and I'm somewhat imbalanced (which would be considered a good next step in the interaction...) my tendency is to stay in "solid" mode -- thinking about it now as I write, I'm probably momentarily freezing? tensing?
From your description, I see the problem there - that you're 'reaching a goal' and so stopping momentarily before starting something else - following/blending with uke. Very possibly its not a matter of physical tension, just a pause where you have to switch to a new task.
I'd suggest to think about the concept of Continuous Attack, that's been mentioned above. This can mean pushing on towards nage, or beginning a second strike, or moving to recover your center in order to strike again. Personally I try to keep the feeling of wanting a second strike, so that my attacks can be committed AND continuous - without the feeling that something is 'over' when the first strike fails to connect (usually