I am really enjoying the conversation with Mike, as we both explore the design of shelf layout “benchwork”.
In my three studies, I reasoned that a base that works out at 1-1/2” thick seems to work. I arrived at that thickness (dimension) based on three plies of half inch foam sheet. This provides enough for: a raceway to store wires under the layout, plus a top layer I can cut into for land forms, plus a middle layer of cake that connects it all together. These layouts all live on top of bookcase units. I like the idea of the layout’s footprint as a loose form arranged across that top.
If I can further reduce the thickness of the layout base to something in the region of a half inch (maybe even thinner?) it reduces a shadow created in the perpendicular regions between the case top (horizontal) and layout edge (vertical). Also, as I layer crude forms together in this space, reducing this vertical dimension allows the layout to retain its free shape but gain some horizontal mass from the case below. They start to correlate as a cohesive form without losing any of their individual identity as different things.
Categories: How I think, model railway design
Prince Street 
I love these sketches.
Is that shadow at the front, or the back of the layout?
Where is the light source, how are we controlling that important aspect on our composition?
Thin board edges and the appearance of the layout floating, yet appearing as one with the shelf. What colour do you paint the edge of the board, the landscape as if sliced through with a cake knife? A lovely slice of cake. Perhaps chocolate?
“Shadow” here has two interpretations.
The very real shadows created by the relationship of light and the forms it interacts with. Observing the current studies or the layouts that preceded them in this same room has catalyzed my decision that all the light I need as the layout’s main light source is what’s washing in from the windows. As the sun moves around the Earth it looks in, through our windows, from different vantage points so plays with this scene in different ways. Referring back to my drawing, shadows that collect on the fascia of the layout soften its transition from in the layout “container” (the modelled scene) to the space beyond.
The current 1-1/2” thick base also creates a segregating shadow. The top of the bookcase is about a foot deep but my layout lives in a region of six to eight inches of that. The thickness of the base elevates the layout like layers on a wedding cake. These proportions seem to underscore the narrow width of the layout because the narrow layout is stacked on a narrow shelf. If I thin the base down (think closer to the half inch-ish thickness of your Pont-y-Dulais) the top face “layout” is closer to the top face of the shelf it lives on. As the layout gets thinner the division between both regions blurs and the layout doesn’t feel as narrow since its perimeter blurs into its supporting element’s perimeter. A figurative “shadow”.
I’ll confess that while I absolutely can not ever be trusted around a Fruit and Nut Bar or a Kit Kat I mostly don’t eat a lot of chocolate but I am a huge fan of a good old Victoria Sponge. So, subtle vanilla, warm butter, and raspberry jam flavours.
Chris