I was at a Yin class recently and we did Shoelace pose. On my upper leg I noticed my foot was sickled. Go to this link http://www.yogadancer.com/Pattra/Padmasana.shtml#Full first picture to see this. That is a picture of a different pose but my foot was bent in that same way. I engaged the muscles in my leg to straighten this alignment. But this was Yin so when I would relax the muscles the foot would sickle.
I have learned to 'never, ever sickle the foot' just like the link. I asked the teacher and she said straighten the foot so we went through this again and never did resolve the issue.
It didn't seem to put pressure on my knee and didn't seem to be an issue. Is there instructions for dealing with this in Yin?