Here is a quickie adjustment you can make in Savasana to help some of your students find a more comfortable position and a more relaxing Savasana. Have you noticed that when you lie down flat to move into Savasana your pelvis wants to tip anteriorly, creating a stronger lower back arch? In Savasana you need to consciously tuck the tail a bit to be in the neutral position the lower back needs to release fully.
For about 20% of your students (my guess based on my experience), their psoas, the deep hip flexor muscle, is too tight to be able get a good enough tuck to release the back. When you watch, they can keep their pelvis neutral/level with the floor until their legs are almost fully straight. As they take their legs that last little bit, the pelvis tips and the lower back pops up. (I am in that 20% of people). With the lower back over-arched, tension creeps in, whether or not they are aware of it. I still don’t feel tension – which is why I never noticed for the first decade of my practice. What I do feel now is that the energy flow isn’t there when my back is arched.
All you need to do to help them is to place a folded blanket under their thighs. Ahhh…heaven.