Braulio Estima didn’t invent the inverted triangle, but he sure did popularize it. With his ADCC win in 2009 over Xande (and his attempt on Galvao that made magazine covers) Braulio sunk the choke into Jiu Jitsu’s subconscious. Aside from this hip clamp another great way to get into it is from spider guard. Same principle except your legs are already up and clear. Give it a shot.