I also did some quasi-universal observation like that each symbol has either two shells or at least two spikes (with exception of electrum, #19 and #22) or that the relative arrangement of the curves and spikes is in some way conserved (especially when looking at the cadmium-bendalloy, chromium-nicrosil or aluminium-duralumin pairs), but the only rule that seems to appear everywhere is as follows:
The pushing metals have the dot inside the curves. The pulling metals have it either outside (tin) or on the circumference.
What bugs me is whether the unknown symbols stand for some additional metals or are just fillers. And if the former, are they pure non-god metals (thus breaking the rule of 16), pure god metals (but then, where do they come from?) or some additional alloys, e.g. of atium (less logical, less systematic, but makes sense after all). Has there been some discussion about it on the forum I have missed?