Chen Style Taijiquan and Xin Yi Ba 心意把

We all know that the various styles of taiji developed from Chen style taiji. However, from where did Chen style taiji develop from?

Matsuda Ryuchi 松田隆智 has his own theory about the development of taijiquan. He sees a connection between Chen style taiji, and Shaolin's Xin Yi Ba 心意把.

As you can see, figures 3 and 4 are similar to Chen style's 金刚捣堆, if not the same. Yet it is not in other styles of taiji, such as Yang and Sun styles. Why? Could it be that this move was only added into Chen style after Yang style was borned?

掩手耾拳 - Which Leg To Put Your Weight On

Is 掩手耾拳 a reverse thrust (karate's gyaku-tsuki 逆突き)? According to the books on Chen style taiji that I have, they all state that the punch is performed with the right hand, with the weight on the left leg. Yet, my teacher teaches me to punch with the right hand, with the weight on the back (right) leg. His reason being that if your weight is in the direction of your punch, you can easily lose your balance, something which your opponent can easily use against you. Your weight can be on whichever leg, since the power from your legs can be directed by your waist to your arms. Putting your weight on the back leg gives you a more stable punch without compromising on the power of your punch.

I ask this question because I was reading a book by Matsuda Ryuchi 松田隆智, author of the Japanese manga "Kenji" ＜拳児＞. In his book ＜続・拳遊記＞, he showed examples of 掩手耾拳, and mentioned that when he learnt it, he was taught that the back (right) leg is straight, rather than slightly bent (like what is being taught nowadays). He feels that the straightened back leg adds to the power of the punch, and that is true if 掩手耾拳 is to be done like a karate's reverse thrust.

A picture of Chen Xiaowang's 掩手耾拳. (From http://www.taoistsanctuary.org/taijiquan/maintaiji.htm)