As per the classical Triangle pose (Trikonasan) the front heel is aligned with the arch of the back foot. However in Intense Side Stretch pose if the back of the legs, hips or lower back are tight the classical version (A) is not possible without loosing the integrity of the pose and distorting the shape (e.g. the back hip will not move forward, the back will be twisted etc…). In this case we may step the back foot slightly to the side to place the heel (instead of the arch) in line with with the front heel (B). If we need further space for the hips to come square then we can place the feet hip width apart (B front foot & C back foot)
Seek Mountain pose (Tadasana) in your feet (four corners pressed down evenly). Broaden the soles of your feet, find the space between your toes spreading them wide and lengthen your toes forward.
Action of front foot
The tendency is to let the weight go to the outer edge of the foot, rolling the foot/ankle out hence loosing the balance. Press the inner edge of the foot down strongly; the base of the big toe and the inner heel (near the arch)
Action of the back foot: The tendency is to let the weight go to the inner edge of the foot, collapsing the arch. Press the outer edge of the heel down strongly, and keep the inner arch lifted.