I'm wondering if this whole discussion of kamae is too limited. Surely you don't just assume a kamae and wait for someone to clobber you? Surely you move from kamae to kamae throughout the encounter, starting from before your attacker moves into striking range? (Unless you're taken by surprise, of course.) So really, the question is, what's the appropriate kamae to move into to receive the initial attack? And that, of course, will depend entirely on what the initial attack is.
I understand kamae as a training tool that strongly influence the conditioning of your body AND influence the way how you execute the techniques. So the choice of some strange kamae will distort the techniques. As a consequence it will deform the content that those techniques are supposed to build in students' body. So transmission of the Founder legacy will no longer be possible.
Coming back to your question, every technique have similar stages, and the moment of interception of the attack is only one of them. The requirement of each stage is different when it comes to kamae so you must understand it, learn and know how to apply automatically in different circumstances. It will not come in spontaneous way; it is a conscious learning process.