Being in an upright, open, forwards position avoiding being on YOUR back which requires YOUR baby navigating a curve in the birth canal. This is hard work. YOU want gravity to help.
Being on your back restricts the sacrum and coccyx to do it’s magic. The coccyx needs to move out of the way, so the baby can pass through.
At the end of the day … listen to YOUR body – it knows where it’s comfortable & what works for you.
Exploring various positions. See the diagrams