It's possible to apply 'weights' to NPS campaigns grouped together under a tag.

Once weighting on your account (please request via Support if you want this advanced feature) is enabled the ' Campaign Math' option is made available to apply weights to all the campaigns listed under a tag.

The sum of weights must add up to 1.

In the example below - the selected tag has two campaigns, Home and Travel, and these campaigns have been applied weights of 0.68 and 0.32.  

The chart type must be set to npsbar to view the weighted NPS.