While I was out on the weekend acquiring my table-leaf fasteners, I also picked up fasteners for the fasteners as well as assorted hardware and materials for constructing the backdrop and lighting valance. I have a rough plan in mind but I wanted to verify the height of the lower edge of the valance and the top edge of the backdrop. While I was at it, I got out the LED strip that I plan to light things with.
Here is the whole mockup in final form lit only by the LED strip. It looks reasonably bright in the photo but in person I found it a bit dim. I will have to consider a second strip although normally the room lights will also be in play.
I determined that the top edge of the backdrop is visible to anyone about 5’4″ or shorter. From what I can tell from photos of UK model railway exhibition layouts, obscuring the top edge of the backscene is not considered absolutely necessary. The backdrop as mocked up uses two foot wide material so I think this is a reasonable compromise.
Here is the mockup with the room lights on just for the curious. Note that I do not intend to have a pink coloured backdrop.