After peeking at the hints it seems that you can add the column of such a declarative index directly on the query tab. This create the necessary Declarative Index Join reference. However, it uses a prefix "Index_WorkHistory" identical to the name of the rule; hardly a "prefix" in that sense, which confuses me. Is that mandatory?

Other examples shows in this course use a simpler acronym like "PO" for Purchase Order. So, I've replace the prefix with "WH". That seems to work.

Question remain: Why does PRPC clean up those Join references when not used on the Query tab in contrast to the behavior elsewhere, i.e. the Parameters tab?

Also, when taking the logical approach of "define before use" which is common in computer science, one cannot use the auto-complete feature on the Query tab. PRPC has no way of knowing the Join and its prefix, because we must not save before going to the Query tab and make the definition complete. One has to remember the page list properties. Although not impossible of course, it does defeat the purpose of having those auto-complete textboxes, doesn't it?

Some room for improvement regarding Reporting. Or does anyone know a a better solution for defining Data Access for these rules?

I checked into your question, and this is working as designed. If you have index references that are not used in a report, the generated SQL is slower and impacts performance.