I have hopped from island to island, Tormenta to Congrejos, low enemies to high enemies, it all appears random. I do believe that red tagged enemies will yield a better chance at a relic, but random blasting of different leveled enemies gives you a good chance as well.
I see no real method to Disney's madness, but I try to have as much fun as I can running and gunning through different places. Keep after it, I'll see ya's out there.
