Okay, seriously...who told my instructors that I have been trolling on the forums about aiki-ken without having actually done Saito's kata? Because just last night I actually did a couple of them for the first time.
The teacher just stands there giving the student a target and forcus, he holds his sword horizontally over his brow, as I was told, to just give a focus and so teacher is not constantly bokked on the head by unfocused student technique.
Somehow, with some, this seems to have turned into a 'block', and IMO a very innefectual one, Some have realised this and tried to turn it into a better 'block' thus defeating the purpose (?) of the exercise in the first place? *
I think what is happening here is the instructor is executing a technique called a nagashi
that is present in Shinkage ryu and Kashima styles. It's not a block in the sense that you apply counterforce to halt your opponents attack. It's more a way to negate an attack in such a way that an opening is created that can be instantly exploited.
I believe you are correct that there is a lot going on about maai and that both partners are supposed to maintain a certain maai throughout the kata. This probably means that the nagashi is never "fully realized." But it is still THERE, in a way that traditional kumitachi have layers of unrevealed techniques.
Anyway, some visual aids. First, I think what you are referring to is what the guy on the right does at about 00:18 of this clip:
Now look at what the guy on the right (but actually both of them) do at about 00:16 of this clip of Kashima Shinto Ryu: