Single board is a transitional cross-legged method to exercise double boards. The purpose is to exercise the flexibility of legs in turn and finally realize double boards. You must put your foot on the thigh root of the other leg in the double dish, so it is the same in the single dish. I totally understand what you said about putting your feet on your calves, because not putting your feet on your thighs will reduce the pain in the initial training and help you to be quiet, but it can't achieve the purpose of stretching your legs, so if you want to improve, you have to make the movements standard and put your feet on your thighs.