Telerik Reporting does not support overlapping elements from different report sections. The size of an item cannot exceed the size of its parent report section. Therefore, the items inside the footer will always be rendered below the detail section.
You can review Design Considerations for Report Item Layout
help article that might give you some ideas for the layout.
If you need a text displayed in the background, check the options available through the Watermarks
You can also set a background image for the report e.g. use the report's Style.BackgroundImage which is visible in both interactive and print preview
of the document, or use the report's PageSettings.BackgroundImage which is visible only in the print preview of the document.
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Feedback Portal
and vote to affect the priority of the items