CC2 Trifecta – N-Hold question

Quick question. Been easing into N-hold with the help of some previous advice on forum, making it to ten second holds. However, I recently noticed that in the book the picture seems to imply that your knees should stay together in the hold. When I perform the hold, however, I cannot help but frog my legs/knees outward (forms a diamond with legs). Does this defeat the purpose of the stretch? And if so, any ideas how to prevent it?