My teacher always taught me to observe what was happening in your yoga poses. Every little thing we do has repercussions. Can we train ourselves to observe these differences? For example, what difference does it make where you place the strap on your foot in Hand to Big Toe Pose?
If you place the strap on your heel, the sensations will be transmitted through your heel down into the bones of your leg. See if you can feel this line of energy. Remember to keep your leg straight.
If you place the belt on the ball of your foot, the force will be transmitted into the muscles on the back of your leg; into the calf and hamstrings. This can be intense and if your hamstrings are sore, I would not do this version.
If you place the strap in the arch of your foot, you should feel the stretch balanced in the center of your leg. Try it here and see if you can feel that sensation of the whole leg working.
Yoga is about the development of consciousness. Can you develop your consciousness to detect the differences in where you place the belt on your foot? Once you start to learn to see and feel these differences, you will be entering into a deeper state of your yoga practice. As BKS Iyengar said: “Yoga does not just change the way we see things, it transforms the person who sees.