I have a crazy sense of smell. I totaly get what you're saying. Karma definitaly has 'his' smell and when it's mixed with someone elses it definitaly seems off to me.
My sense is so strong it will also effect me physicaly. There are certain places Karma goes that when he comes home he showers right away and the clothes immediatly go in the hamper. Migraines and even physical illness have resulted from it. And we avoid perfume shops, bath and body stores, candle stores all for the same reason.
So while I love that I can sense people with my nose, its a double edged sword for me.