Head alignment in kua squat

Hi Paul,
I would like to ask a question about the position of the head during the kua squat. I am sorry if it was mentioned and I overlooked this information.
Should the head be on the same line with shoulders and feet or can it go a bit forward during the kua squat? I found that I can do both but with the head slightly forward it is much easier.
Another question: there is the so-called wall-squat popular in China, when you perform a squat with your toes, knees and a nose touching the wall. I practiced it before I started this course. Are they similar? Would you recommend it or not?
Thanks a lot for your help!
Alex