I am having the same problem with Change requests. We have an approval email that I have included key data on. Sometimes people include attachments into the change request and approvers want to see via email vs. having to log into the system. This mostly comes into play when they are using their phone and want to just reply to the email with their approval. But by not seeing the attachments, there is concern they are missing valuable details for their decision. I see the box you have in your screenshot. but I only get Journal.email as an object choice. I would guess I'd want to see Change?
Update. I'm fixed.
I had to create a relationship in the Approval Vote tracking business object to see Change. My guess for Jeffrey is you need to create a relationship link to the Parent for Incident. As you see in mine, my email is coming from approval vote tracking business object.
I would look at your communication Manager and see what drop down you are using. I had to essentially point that to the parent of Change.
Hope this helps
Have you tried using what was in your screenshot? From my testing on 2015.2.1, that configuration should attach every attachment directly on the incident to the email. It would not pickup attachments on tasks or emails. Is that what you were looking for?