I have the following Transaction Flow diagram:
Inspecting the First Party Content - User Action PurePaths I see this:
In the details of the first Loading of page I see the beggining of Source URL and Target URL as http://mhop/MHO_Prod/...
As for the Application configuration, all URL starts with http://mhop/ should be in the same application, and all these URIs are hosted in MHO_Backend.
The question is, why there is not an arrow between FIrst Part Content and MHO_Backend? MHO_Backend is hosting the application (http://mhop/) so in that Loading request for those pages, it should have been impacted.
I think it might just show as first party content because the elements that it needed to load the page could have been cached. This would mean that I wouldn't need to reach out to the backend app server to load the elements needed to render the page.
You can test this by clearing your cache and performing a visit. I am guessing the first party content will disappear as all the requests will have to hit the backend.