Easy fix for now - edit the Starfield.ini directly in the game's root folder, instead of StarfieldCustom.ini. Nobody seems to know why the custom INI doesn't work across the board, but it's well established that it doesn't work for everyone. I've also read that textures don't load outside of "My Games\Starfield\Data", while other assets will. I chose not to trust this information, and simply installed mods in both locations - the root Data folder, and the "My Games" Data folder.