It's an optical illusion. They extend enough past the props to protect them from most things. I don't have a shot from directly above, but The photo just above where I put up the pictures of them on my quad, if you look at the bottom right prop which is closes , and imagine rotating that prop, you'll see there's probably a cm or more clearance, but I'll grab some pics next time I have it out for a fly. Hopefully tomorrow after work.