Good question, Les! I plan to include a more detailed breakdown/progression for this move (and lots of others!) in my next book, tentatively set for release in 2015.
Basically the more contact you have between your arms and legs, the easier the move becomes. Also, the more you bend your elbows, the easier it will be. So the most regressed version is with a deep elbow bend and lots of arm and leg contact, the most advanced version is with the elbows locked and very little contact between the arms and legs, which eventually becomes the tucked planche, which is quite advanced as Robby mentioned.