When I train my LF, my teacher always required me to keep my heel down in a bow arrow stance. One day I asked him why we kept our heel up in a monkey stance, his answer was "it's different posture". I then asked what if we are changing from a bow arrow stance into a monkey stance, should the heel be down or up? I didn't get a good answer for that.
We cannot discussion certain requirement in CMA without good combat reason. I just don't know the purpose of keeping the heels down. You will need to raise your heel, if you need to:
- spring,
- throw, or
- kick sand back at your opponent's face when he chases you from behind.
Unless you just want to slide your foot on the ground for inner and outer leg bite. If it's for "health" purpose then I don't think it matters whether you keep your heels down or up.