Hello Tim,
There are three things I see within your post.
The first is the differences from one style of asana to another. Those things are best answered by the person you have chosen to teach you yoga. When you go to a class you have selected a teacher, either for a reason, a season, or a lifetime. You did not mention if this was a workshop or a level 5 class AND my curiosity as to why the room was filled with teachers is piqued. Generally, it depends on how the THAT practice (in this case Anusara) is crafted and since I do not practice nor teach in that style I simply cannot say.
The second thing is the idea of a “valid” asana or position. Valid to whom? In What context? Again what might be valid for Bikram may not be valid for Ashtanga. I tell my students that there are some things that are inherently wrong (based on yoga philosophy) and other things that are merely differences in this school or that school of thought/practice. How to know which is which is the “trick”.
In Purna Yoga which falls in the lineage of BKS Iyengar and Sri Aurobindo, the placement of the head for a healthy student for Sirsasana is the front fontanel of the skull.
The third element is your perception of risky and dangerous asana practice. Whether it IS or is NOT so, your perception is your perception. And so I would advise a student of mine who felt like an instruction, a pose, or a practice was unsafe to express that to the teacher, not do it, or find a practice that more suits their sense of safety - a completely appropriate direction for a student of yoga.
