Placing Marignon in Amn would be a much more thematically correct choice, especially given how Amn or some portions of it were depicted in the Maztica trilogy.
You could also put some space into eastern edge of the map by moving C'tis to Unther (which is the same as Mulhorand, but modeled on Sumeria/Assyria/Babylon instead of Egypt) and tossing Ermor into the Plains of Purple Dust. It would probably still be too crowded, though. It's a shame the map doesn't extend all the way to Kara-Tur, I would have loved making a map of
that. In such a setting, Ermor would have ended up in the Raurin desert, because that does have a lot of buried necropolises from the precursor empire of Mulhorand that annihilated itself in a war against its gods. As it was, I had to put Ermor in Anauroch which has a significant number of Netherese ruins.
Good luck with the project, it looks to be a stupendous undertaking. And thanks for the kind comments on the original map.
Edi