There is an option in the activity to Generate URLs that says if the entry is an electronic document, then use the web client settings.
So when you read more about this setting, it has a hyperlink
The hyperlink takes you to this instruction
But we don't see Document Viewer under Options. These are the only options categories.
Everyone eventually lands on the Display tab (shown below) and assumes this is the right place, which it is not. With testing we find that these settings apply to the DocView.aspx website and not the ElectronicFile.aspx which is the aspx file we are working with when generating these types of URLs.
The breaking point is the missing Document Viewer category in the current version of Web Client, currently this environment is on 11.1.2212.409
So now we are just clicking around making assumptions as to which settings it is using.