the healing priority should be like this:
Cure 30-40% > -na > Cure 60-70%
you see, if it was only Cure > -na there is a very high chnace that the AI will get stuck on cure without casting a single -na even when you are safe, I faced this issue when i was trying to build my healing gambit in FFXII, It can be different though or not needed here, but this method of AI healing is the most logical way I can think of and work perfectly in other games.