As you already know, there are other systems influencing
Hung Kyun, but if you are talking movements from the GJFFK, TSK, and most of FHSYK, in
Ji Ng Mah/ "Forward Bow Stance", we pivot from the heel...
From
Bat Fun Mah/ "Offset Horse", the front foot is already set at the desired angle, so only necessary to pivot on the rear, not both feet pivoting simultaneously like "windshield wipers", ok...
In stance-to-stance transitioning movement (like
any movement), it is important to train in a progressive buildup...
Here, try this little exercise:
1) Facing toward a wall, "approximate" a Forward Bow Stance, with rear-hand
Ping Choi knuckles lightly pressing into the wall at middle target level...
2) Turn out your back foot until your toes are now positioned at 90 degrees, should now be parallel to the wall, your fist pointed forward, but no longer in contact. Letting your hips settle into place, you now are in the
Bat Fun Mah position...
3) From
Bat Fun Mah (with knuckles of your (rear hand) fist extended toward the wall), raise the toes of your rear foot clear and away from the ground. This is to make sure there is not any weight transfer whatsoever to the ball of the foot, at any time during your forward pivot...
4) Pivot to your Forward Bow, the knees should straighten just as your fist turns over, contacting the wall. This "screws you in" to all three points of contact...
5) Execute this drill in repetitions, and/ or hold position for 30 seconds at a time on up...
Just think about it, the
Tibia/ Fibula (lower leg bones) connect directly to the point of the heel. That means that only the knee joint remains to be managed between the hip socket, and the point of grounded contact/ force transmission. Much more stable, reliable, and efficient than adding in the extra angle (of the ankle joint), which additionally offsets your point of grounded contact from your line of force transmission by as much as a "foot"!
Best,
Michael