Rob, thank you for the clarification and for sending the screenshots.
Based on the layout you described, there is no rendering issue. The page is displaying according to how it was structured:
- In your first section you divided the row into two columns (9 + 3).
- The Joomla module is placed inside the last column of that same section.
- After that, you created a second section containing an image.
Because those are two separate sections, the module column will always end where the first section ends, and the second section will naturally start below it. This is why you are seeing vertical space between the first and second sections. The system is not treating the module as a persistent sidebar—it's simply occupying its column within a single section.
If your intention is to have a persistent vertical panel at the right side that spans the full height of the detail view, all the content that should align next to it must be placed within the same section. A sidebar cannot span multiple separate sections; the structure has to be unified within one section layout.
Regarding linking the detail view to a hidden menu item: linking dynamic content detail pages to a menu item is not possible. Detail pages generated dynamically do not create standalone menu items that you can target for module assignment.