Drew - you are right we haven't trained togeather so all I can base my opinions on is what you write.
The statement I took exception to was
What we typically call "proper ma-ai" is the best distance for us to train.
Which implies that ma ai in a training environment should somehow be different.
I also don't think that you could describe the distance between any two combatants at any time as ma ai either. Ma ai is an ideal point which varies depending on a number of factors. These include size, weapons and type of combat. For example, all other things being equal, both Judo and Aikido have different ma ai. If you are too far away you are not in ma ai - too close same problem.