I use those files by placing them in my game folder, so I set the textures (.dds files) to the "Textures\" just so I could avoid having a mess in the game folder, plus on the other hand it's quite handy to be able distinct the textures from the models in the import manager, so when you have a large amount of textures and models it won't be as annoying to navigate. You can set the models to whichever path you prefer, just be mindful that both base model and _Portrait need to be in the same directory.