Thank you for the inquiry about this matter.

Let me share with you some info regarding Persian Positions.

You could probably decide that the value of the invested troops has not corresponded to your gains lately. And this, probably, was what made you reach us out. I hasten to dispel your worries about a bug that could creep into this functionality. The dev team keeps Persian Positions under the constant thorough control at all stages. 

As you know, I am sure, after every victory, there is a gap that gets generated and which you need to fill with units gradually in order to be able to win again. What is also important to remember here is that Positions are not designed for raising the number of your army, but for converting weaker units into stronger ones primarily. I would recommend taking a break from Positions, concentrating on building the troops that you would not feel sorry about losing later on Positions.