Hi @rbiri ,
You can try the below query configuration,

Targeting Dimension: nms:delivery
Filtering Dimension: nms:delivery
Query:
@created on or after DaysAgo(30)

In my case, in preview tab,

So the expected average of deliveryCode2 is 2 and deliveryCode3 is 3 and deliveryCode4 is 4.
Complementary information > add data >
- select delivery code (@deliveryCode)
- Add an expression > Avg([indicators/@success])
Click Group check box on @deliveryCode alone > finish > save the query

Reopen the query > edit additional data > advanced parameter > do the configuration as below,

And run the workflow,
The output:

Received the expected average success per delivery code on last 30 days.