Just to throw it out there...that Rickson did not teach the armbar at the Torrence academy like Pedro Sauer did in that video. Im not saying that its wrong or anything. Just not what he emphasized this last saturday. I had seen that video before the seminar and was expecting something similar but was surprised. I found Ricksons very interesting.
Rickson also did not address the setup. He started from when the arm was across (basically, giving the opponent the armlock to see the armlock technique) in an attempt to illustrate a concept by how he positioned his legs to now allow his opponent to stack him. This was of utmost importance to him and his attention was focused on having the arm already extended by the time the leg comes around.
Assuming you are doing the armbar on your opponents right arm, He threw his hips up and locked the left shoulder...BUT without crossing the legs. His left leg clamped down on his opponents right shoulder. The right leg went into his armpit and both clamped down and pushed him away slightly. Correct use of the legs made it impossible to begin to stack. It was very interesting indeed. From that point, you wait for the right moment and throw the leg over and his arm will already be extended. He showed several times that you just follow him however he might try and escape and apply the armbar anyway.