I'm not an expert on this by any means but I don't think he's trying to assert any dominence by sleeping on the floor. If anything it may be the opposite. Usually the dominent one will try to elevate themselves higher than the others so him being on the floor would put him lower than you. I used to always try to get my dogs to sleep in bed with me when my husband is gone and they refuse. They would do the same thing Nelson does...just stare at me like I'm insane and then go to sleep on the floor. I finally realized that I'm pretty lucky because they are just getting way to big to share the bed! I wouldn't worry about it too much. My cocker was extremely dominent and she would jump in bed with us. If you tried to move her, she'd snap at you! Talk about bad temperment!