Troop vs Troop problem

I've seen that troops select a target and goes for it until it gets destroyed. When it is destroyed, the troop select a new target and goes for it.
But in case of low life enemies, maybe the target is destroyed before the troop makes its atack. I've seen dragons or wizards stand still in front of a group of archers for long time without doing any attack.

My purpose is: for a multiple-target troop (wizard, dragon, balloon) give the ability to attack a position (or area), so if the target dies, its attack doesn't be interrupted, especially because of the low speed of the attacks of the troops of this kind.

In case of single target troops the problem is the same, but i think that it is logic that if its target dies, the troop would select a new target (giants, pekkas and golems will cause trouble) and because i think that it is.not logic that a pekka blades its.sword in the air.

Sorry for my English. I hope it is understood.
And sorry if repeated, i didn't know how to search this.