Hi,
Is it a custom/standard report you are referring to? When you specify grouping/aggregation it applies to the whole query.Also, you can add the grouping to your report query in the processReport method of DP class. If possible can you share your query(with a screen shot) such that we can better help you.
Refer following link:
(Walkthrough: Creating an AOT Query that has Group By and Having Nodes [AX 2012])