I haven't played the map, but if you have 36 civs on it, even having 18 copper squares on the map means that half the civs wouldn't expect to have any. With such a big map and with so many civs, if you limited the resources to scarce quantities, you could see big imbalances.
South America from the Giant Earth Mod. North America has a similar amount of copper on the west coast, and none (iirc) on the east coast.
Europe, on the other hand, has like 8-10 spots total, and not all the civs get one near them.
Africa has 5 total, one for egypt, and 4 down near the bottom. Middle East gets 2.
India has zero copper spots, same with japan. Australia has at least one, I think.
'Asia'/'Russia' has some peppered throughout.
Edit: To be a bit more on-topic, I've found that building the Forbidden palace isn't an option on huge maps (and especially on GEM): it's a requirement. And that 'useless' Divine Right tech that people seem (to me) to avoid becomes a tantalizing beeline target, or at the very least, something seriously worth considering.
While playing GEM, I've been trying to find a way to maximize the returns I get from building just the Forbidden Palace while my empire is still expanding, and the best I've been able to come up is this.
1: Build the FP near one 'edge' of my land. Preferably an 'edge' that I won't be moving anytime soon. For example, a continent that I control completely, like Africa or Europe or near Japan. My borders can't go any further than that unless I go overseas. Build it slight inland from that 'edge.
2: As I continue to expand away from the edge, and away from the FP, I move my capital in the direction that I'm expanding.
In doing so, I should be able to balance where my 'maintenance reducers' go for the 'best' return possible. One might even consider building Versailles first, and saving the FP for future expansion, but I don't think that is realistic.