Adjectives just don't work in a rigid fashion like that. There isn't a mechanistic process by which you take an adjective and noun combination and apply the one

Adjectives just don't work in a rigid fashion like that. There isn't a mechanistic process by which you take an adjective and noun combination and apply the one and only rule for deriving the meaning of that combination. Life might be simpler if there were, but it doesn't exist. Formal languages work that way, but natural languages don't. Instead, you take the two words you want to put together to mean whatever you want it to mean, and if the meaning is useful and people could figure it out, you're allowed to use it. So, a fake X can be something that isn't really an X. Or it can be something that is really an X but fakeness is involved in some other way. For example, if you meet someone in a bar and ask for their number, and then when you later call them, some totally different person answers, you've been given a fake phone number. The number itself isn't fake. It's a valid number that works fine for placing phone calls. The fakeness is in who the number belongs to. A fake person isn't a being who isn't really a person. It's a person who exhibits fake behavior. A fake voice isn't a sound that wasn't produced by a human vocal tract. It's a voice that is produced by a human vocal tract but it isn't their normal voice. The fakeness is that it intentionally sounds different from their normal voice.