De ai? I suppose you could call it such, I call it timing, but see what you mean. Ma ai does not mean back up so I fail to see that.
I can watch a boxer keeping ma ai and in the end get a warning for not fighting. Boxers are very good at keeping ma ai and most times in a circular fashion. All sensible martial artists use it and enter when the 'opening' presents itself or they cause one to.
The opposite of ma ai is not standing your ground so you lose me there also.
What do you do with a swordsman? Depends how good you are at keeping ma ai doesn't it?
Need I say there is physical ma ai, mental ma ai and spiritual ma ai? .
Ma ai is a noun, not a verb. It simply describes the distance at which both parties are "safe:" neither can actually strike the other without moving. As such, it doesn't really have an "opposite." There are smaller intervals, and larger intervals, but *some* interval always exists.
It is true that ma ai doesn't mean "back up." Backing up is just one way to adjust the distance. My point, however, is that it is not always possible to simply "maintain ma ai" indefinitely. The terrain may not allow it, or you may be in a multiple attacker situation, or your movement may be limited by the need to protect another person. Rather than pretending such situations don't exist, please explain how you approach them.