Honestly, I think slimmness works better. In the people I've seen that pass easily, it's the slim ones. The reason is because we expect women to be smaller and more petite. We're used to seeing obeasts, and we're definitely used to seeing male obeasts, so it's very easy to say, "That's a fat guy." Unless he looks really androgynous, I never confuse a fat man with a fat woman. In other words, even with the fat there is no assistance in passing.