Among all the sources I've read so far (everything except Rumors and Lies), I haven't been able to find much info on the planar cosmology in DragonMech. Just that the Astral or Ethereal (I forget which) sort of surrounds the Prime and connects it to the other planes. And that maybe these other planes might actually be just domains of the more general Spirit World. Or maybe it's just the default Great Wheel. It's kind of vague. But I like it, in a way. It's always stretched my credulity that every supposedly medieval fantasy setting has charted out the planar cosmology in full, when it's not even possible to observe how the various planes are connected. On the other hand, DragonMech isn't a medieval setting. More like Renaissance meets Victorian England/general steampunk era. So I'd more readily believe that they know what's going on. Anyone have any ideas on the planar cosmology? If not, I'm happy to leave it as poorly defined, even to its inhabitants.
But one thing in particular I have decided on. The moon straddles a position between the DragonMech prime and some other, lunar plane. It vacillates back and forth, so that at full moon it's entirely here, new moon it's entirely there, and in between it's partially on both planes. Why introduce this strangeness? Mainly because I'm not convinced that regular lunar cycles could actually affect the lunar rain. After all, new moon versus full moon is a matter of a bad angle for the moon to reflect sunlight from. Clearly the lunar gods have pooled their might to increase the full moon period and decrease the new moon period (or even blot it out - it only gets very close to new moon).
I am Omnirahk, half-Rahkshi ("Omni") of the WotC forums. I consider "Psionics in DragonMech" (see my website) my greatest contribution to anything d20 so far. At least, it's my most successful topic.