It may be a solution of my question.
The answer got from the simply the best , posture, tango , with Marcus .
He mentioned several points in tango comparing with the other dance. (I will use allthese points in my tango and might discuss with my teacher very carefully )I was so glad to hear Karen suggestion about the position of her left elbow and hand . I used it before , then my teacher altered it ,uncomfortable and shorter forearm and hand due to too close his armpit.)
He said : rotate right hip (right knee involved ) INTO THE LEFT . He put hIs both hands on the front of his LEFT pelvis, to make sure the left side does not rotate back. and call it RIGHT SIDE LEADING, same in lady also.more flexed knees , and more flexed ankles. keeping parallel shoulders . IT is different from simple 1/8 left turn. the feeling is right hip rotates forward , presses into left hip, left hip against and absorb the rotation as much as possible. this is the lower part . )
Because it was mentioned in the posture, style part, I thought it had become a character and should be maintaint in all closed position.including stop step following a side step.
Walk , stop are common in tango. Even having right side leading similar in man and lady, additional CBM if needed is acceptable. The main point is RF is on LF line ( lady back walk ), not across it , of cause across the body center line. right toe in . RF back step may heel leading . resultant new alignment is unavoidable either in The Walk , or forward/backward step. I feel more comfortable now.
ylchen