Sensei Nishiyama explained Maai as distance including timing, or as effective distance.
A big part of our training with sensei Nishiyama was dedicated to understanding opponent’s distance, one’s own distance (Issoku –ito, one foot one technique), and according to those distances, using the relationships between those distances, making strategy.
Also, understanding the different distances:
Standard distance, where I can hit my opponent in one technique, but also be able to go out of his range, being able to give him danger, and motivate his attack if needed.
To –ma, (long distance), and Chikama (short distance), and when and how to use either.
Depending on my opponent size, tendencies, quickness, explosiveness and depending on my abilities, I will choose what kind of strategy and distance to adapt.
Aiko San was the one who really made me understand distance, and understand what sensei really meant in his very few words.
She told me that once I found that distance, my distance, no one will be able to get closed to me, she insisted that I must make my territory and than nobody can get pass that space. She made me realize that I was relying on beating the opponent’s speed and power, fighting with him.
With her help I was trying to figure out how not to brawl, not to randomly attack, but using the space and rhythm to create chances, accept the opponent’s attack, and use my technique in the moment that success is most likely, and than at that moment, live or die, give everything.
It is the wrong kind of spirit to give everything and spend your energy all the time, to use power against power, to be suicidal, to brawl, this is not budo way.
A skilful person should have awareness of the situation all the time, read the opponent, use the space and rhythm to make chance, and just in the right moment give everything, hold back nothing, mentally and physically.
Don’t forget that to use distance effectively one has to have good footwork, to make smooth or quick change of space as necessary, and of course perfect timing to utilize any Kyo (space) in the opponent without Gap.