'IP/IS extremists are not welcome here.' lol... Isn't everyone here one or the other in this past year? What a resurgence I would like to add.
Back to topic, I'd like to use two main methods.
One. To shift center vertically and thereby controlling maai from a vertical space instead of the horizontal plane.
Two. To take over his space using an overt or extended kamae (not atemi in a strictest sense) as he comes intruding into your space.
Both ways can be applied for irimi or tenkan. But are shaped differently. And when I do lose control and they recover from kuzushi, which usually happens when you either stop or try to change movement yourself, then it's back to awase again before using 1 typically.
1.Are you talking here about shifting his center or your center? Could you also explain more why you use only vertical in this case? Don't you see here a danger to ground him instead of unbalancing?
2.I don't really understand it, care to explain more?