I'm not sure what you're trying to do here. You see, to me a sky dome should not be shaded with light-sensitive features like an ordinary object. Meaning diffuse and specular reflection should not be involved on the dome's shader, because IT IS THE SOURCE OF THE ILLUMINATION. There is no "specular reflection" off the sky - there is no reflection on the sky - the sky is not an object, but rather a glowing sphere-shaped region.

In all my sky shaders, I generate the color patterns I want with nodes and plug them into the Alternate_Diffuse channel. This channel renders what you plug in, no interpretation. I turn off all the other stuff.

Now if you want to use concentric spheres, and transparency, so you can build up layers of clouds, that's fine. Me - I just blend them in the shader directly and have only one sky sphere to manage at all times.

Theoretically, using multiple sky spheres could let you get some "real world" effects like shadows from one cloud layer falling on the next. In such cases, I'd still set up the "sky" sphere to glow. The "cloud" spheres could then be using Diffuse and Specular effects in the shader. Moving the sun around would produce a different sky then. I'm not sure if Poser can handle the scaling though that would lead to real-life perspective.

Assume your clouds are 1 mile high. The radius of a Poser sphere at 100% scale is 5.16 inches. So the scale you need to set to get the radius to be one mile is 100 * 5280 * 12 / 5.16 which is  1,227,907. IIRC, last time I tried a sphere scaled to over a million percent, it didn't render in the reflections at all - it's like it was too far away to be seen.

Oh and the Poser sphere surely has issues with normals and also its UV map is not right. There is always a seam. I found it better to go into some other tool and generate a new sphere of my own, and imported that. I've had no issues since then.

---

Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)