The army management is clearly lacking an indication for unattached units.
You have to hunt for unattached units, once you find one and add it to your attack window, then the whole army seems to reorganize. I see no clear way how the army gets reorganized. I would expect that when you add a unit to the attack selection that all other units just shift in a way, and that you just can continue from the place where you stopped, hunting for other unattached units. But it seems that once you added a unit that you have to start all over again.
It could be simply solved by adding a simple visual indication on the picture, then you even don't have to waste time to wait on the pop-up of the unit details.
I really hope this will be taken into consideration, otherwise fighting will become a real time-consuming activity and become a real burden. And when a game like this becomes a burden, then the businessplan of the game will completely collapse...