Hi Amy, Each person will have their own experience in their body and how it feels. I cannot tell you a "should" feel. The cue is designed to place one's attention on the sacrum and how imagining how the bone responds to the movement of extension. I do cue this in all prone work.
Thank you for a wonderful class, Madeline! It gave me greater awareness of my own pelvic imbalances and some "ah ha" moments that will help me in my practice going forward. Loved how balanced and grounded I felt after class.