Copy_to or new index for ambiguous mapping

I have a question regarding the changes about mapping in elasticsearch 2.3
I have an index topic that has 2 types topic and tag. Each type has a property 'name' that unfortunately has a different meaning. In person represents the name of the topic and in tag the name of the tag.
I am going to use a lot of aggregations on this index so I am not sure if the right solution is to create a separate index for tag or to use the copy_to and copy the name of the tag into a new field.