Hi Alistair,
The report being generated for all campaign is because you are requesting it to do so.
report generation depends on the ctx parameter. Right now you are specifying the context to be global i.e. all campaigns in the instance.
For specific campaigns, you will have to send the correct parameter.
It is something that required in-depth knowledge of the product and hence I'll leave it for other readers to respond to.
Unfortunately, I don't have the answer to this query.
If it is something urgent, you can take help of Adobe Professional Services, as a request raised to support will also fetch you the same response.
Regards,
Vipul