I did a search on "maai" and came back with 4 pages of results
Paul Kozlovskis wrote:
Besides, 2cm is correct maai when someone is standing 2cm away from you in your face.
I want to disagree with this, but perhaps just from the wording. If someone was standing face to face with me, being threatening, this is not correct ma ai! I've already let them breach that by a long ways.
However, if I have done irimi, I'm now standing 2cm apart from them as a result of my movement and I am in a position where they have to move to continue their attack, then 2cm is correct ma ai.
I believe that correct ma ai is when uke has to take a step to reach you. The ma ai will then continue to change as a result of your movement during the interaction.