The calculation for New POS as you have defined it is looking at each underlying record for the result of a/b and then aggregating the results. i.e., it would go through each record in the region and calculate Deployed / Total Stores Period and then aggregate the results.
What you probably are looking for is SUM(Deployed) / SUM(Total Stores Period)? Is that correct?
It is showing some issue with respect to if condition of aggregate and non-aggregate.Let me see.