Apparently an experienced midwife can tell the difference between the early pushing and the effective pushing when fully dilated. If you have a lip, you can help that last bit dilate without a midwife pushing it back. Obviously changing position helps, getting up and moving, but doing lunges - i.e. one leg on a chair or bench and lunging into the chair or going up/down stairs or a step - the movement of the pelvis can help get that extra bit required to fully dilate.